alloc: Select applicable Tta/Tra

According to TS 45.002, 6.4.2.2 the choice whether Tta or Tra has to
be applied, depends on the medium access mode (currently always
dynamic) and the number of UL/DL slots. Currently either value can be
used which might result in combinations not covered by the spec.

This commit changes find_multi_slots() to skip non-compliant
combinations.

Note that this code will have to be extended, if other medium
access modes are implemented.

Sponsored-by: On-Waves ehf
diff --git a/tests/alloc/AllocTest.ok b/tests/alloc/AllocTest.ok
index 00cff6e..cdc6335 100644
--- a/tests/alloc/AllocTest.ok
+++ b/tests/alloc/AllocTest.ok
@@ -8684,8 +8684,8 @@
  TBF[24] class 12 reserves ...DCD..
  TBF[25] class 12 reserves .....DCD
  TBF[26] class 12 reserves ...DDCD.
- TBF[27] class 12 reserves ....DDDC
- TBF[28] class 12 reserves ...CD...
+ TBF[27] class 12 reserves ...CD...
+ TBF[28] class 12 reserves .....DDC
  TBF[29] class 12 reserves ...CD...
  TBF[30] class 12 reserves ...CD...
  TBF[31] class 12 reserves ...CD...
@@ -8752,8 +8752,8 @@
  TBF[24] class 25 reserves ....DDCD
  TBF[25] class 26 reserves ...DCDD.
  TBF[26] class 27 reserves ....DCDD
- TBF[27] class 28 reserves ...DDDDC
- TBF[28] class 29 reserves ...DDDDC
+ TBF[27] class 28 reserves .....DDC
+ TBF[28] class 29 reserves .....DDC
  TBF[29] class 1 reserves ...C....
  TBF[30] class 2 reserves ......DC
  TBF[31] class 3 reserves ...C....