alloc: Use least reserved PDCH for algo A

Currently the slot selection of algorithm A is based on the current
slot usage by active TBF. Especially in the Dl after UL case which
reflects the commen use case "MS initiates TCP connection", the
resulting distribution is not optimal with respect to PDCH usage.

This commit changes the implementation to use the slot reservation
information instead.

Sponsored-by: On-Waves ehf
diff --git a/tests/alloc/AllocTest.ok b/tests/alloc/AllocTest.ok
index 231b42f..00cff6e 100644
--- a/tests/alloc/AllocTest.ok
+++ b/tests/alloc/AllocTest.ok
@@ -8828,37 +8828,37 @@
   Successfully allocated 32 UL TBFs
 Going to test assignment with many TBF, algorithm A (DL after UL)
  TBF[0] class 1 reserves ...C....
- TBF[1] class 1 reserves ...C....
- TBF[2] class 1 reserves ...C....
- TBF[3] class 1 reserves ...C....
- TBF[4] class 1 reserves ...C....
+ TBF[1] class 1 reserves ....C...
+ TBF[2] class 1 reserves .....C..
+ TBF[3] class 1 reserves ......C.
+ TBF[4] class 1 reserves .......C
  TBF[5] class 1 reserves ...C....
- TBF[6] class 1 reserves ...C....
- TBF[7] class 1 reserves ...C....
- TBF[8] class 1 reserves ...C....
- TBF[9] class 1 reserves ...C....
+ TBF[6] class 1 reserves ....C...
+ TBF[7] class 1 reserves .....C..
+ TBF[8] class 1 reserves ......C.
+ TBF[9] class 1 reserves .......C
  TBF[10] class 1 reserves ...C....
- TBF[11] class 1 reserves ...C....
- TBF[12] class 1 reserves ...C....
- TBF[13] class 1 reserves ...C....
- TBF[14] class 1 reserves ...C....
+ TBF[11] class 1 reserves ....C...
+ TBF[12] class 1 reserves .....C..
+ TBF[13] class 1 reserves ......C.
+ TBF[14] class 1 reserves .......C
  TBF[15] class 1 reserves ...C....
- TBF[16] class 1 reserves ...C....
- TBF[17] class 1 reserves ...C....
- TBF[18] class 1 reserves ...C....
- TBF[19] class 1 reserves ...C....
+ TBF[16] class 1 reserves ....C...
+ TBF[17] class 1 reserves .....C..
+ TBF[18] class 1 reserves ......C.
+ TBF[19] class 1 reserves .......C
  TBF[20] class 1 reserves ...C....
- TBF[21] class 1 reserves ...C....
- TBF[22] class 1 reserves ...C....
- TBF[23] class 1 reserves ...C....
- TBF[24] class 1 reserves ...C....
+ TBF[21] class 1 reserves ....C...
+ TBF[22] class 1 reserves .....C..
+ TBF[23] class 1 reserves ......C.
+ TBF[24] class 1 reserves .......C
  TBF[25] class 1 reserves ...C....
- TBF[26] class 1 reserves ...C....
- TBF[27] class 1 reserves ...C....
- TBF[28] class 1 reserves ...C....
- TBF[29] class 1 reserves ...C....
+ TBF[26] class 1 reserves ....C...
+ TBF[27] class 1 reserves .....C..
+ TBF[28] class 1 reserves ......C.
+ TBF[29] class 1 reserves .......C
  TBF[30] class 1 reserves ...C....
- TBF[31] class 1 reserves ...C....
+ TBF[31] class 1 reserves ....C...
   Successfully allocated 32 UL TBFs
 Going to test assignment with many TBF, algorithm B class 10 (DL after UL)
  TBF[0] class 10 reserves ...DDCD.
@@ -8896,13 +8896,38 @@
   Successfully allocated 32 UL TBFs
 Going to test assignment with many TBF, algorithm A (UL after DL)
  TBF[0] class 1 reserves ...U....
- TBF[1] class 1 reserves ...U....
- TBF[2] class 1 reserves ...U....
- TBF[3] class 1 reserves ...U....
- TBF[4] class 1 reserves ...U....
+ TBF[1] class 1 reserves ....U...
+ TBF[2] class 1 reserves .....U..
+ TBF[3] class 1 reserves ......U.
+ TBF[4] class 1 reserves .......U
  TBF[5] class 1 reserves ...U....
- TBF[6] class 1 reserves ...U....
-  Successfully allocated 7 UL TBFs
+ TBF[6] class 1 reserves ....U...
+ TBF[7] class 1 reserves .....U..
+ TBF[8] class 1 reserves ......U.
+ TBF[9] class 1 reserves .......U
+ TBF[10] class 1 reserves ...U....
+ TBF[11] class 1 reserves ....U...
+ TBF[12] class 1 reserves .....U..
+ TBF[13] class 1 reserves ......U.
+ TBF[14] class 1 reserves .......U
+ TBF[15] class 1 reserves ...U....
+ TBF[16] class 1 reserves ....U...
+ TBF[17] class 1 reserves .....U..
+ TBF[18] class 1 reserves ......U.
+ TBF[19] class 1 reserves .......U
+ TBF[20] class 1 reserves ...U....
+ TBF[21] class 1 reserves ....U...
+ TBF[22] class 1 reserves .....U..
+ TBF[23] class 1 reserves ......U.
+ TBF[24] class 1 reserves .......U
+ TBF[25] class 1 reserves ...U....
+ TBF[26] class 1 reserves ....U...
+ TBF[27] class 1 reserves .....U..
+ TBF[28] class 1 reserves ......U.
+ TBF[29] class 1 reserves .......U
+ TBF[30] class 1 reserves ...U....
+ TBF[31] class 1 reserves ....U...
+  Successfully allocated 32 UL TBFs
 Going to test assignment with many TBF, algorithm B class 10 (UL after DL)
  TBF[0] class 10 reserves .....U..
  TBF[1] class 10 reserves ......U.