tbf: Move TFI selection into alloc_algorithm

Currently the TFI and the TRX have to be determined before the actual TBF
allocation function is called, passing TFI and TRX number as
parameters. This does fit to TFI reuse for different slots, since
this were tightly coupled with the slot selection.

This commit just moves the TFI selection into the alloc_algorithm
functions. The tfi parameter is removed from the the TFI alloc
functions. The trx parameter is changed into use_trx to optionally
limit the trx selection (same semantics like in tfi_find_free).

Sponsored-by: On-Waves ehf
diff --git a/tests/alloc/AllocTest.err b/tests/alloc/AllocTest.err
index 2dc99fe..d848aff 100644
--- a/tests/alloc/AllocTest.err
+++ b/tests/alloc/AllocTest.err
@@ -1,36 +1,55 @@
 No TFI available.
 No TFI available.
-- Failed to allocate a TS, no USF available
 No TFI available.
-No TFI available.
+- Failed to allocate a TFI
 - Failed to allocate a TS, no USF available
 No TFI available.
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
+- Failed to allocate a TS, no USF available
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
 No TFI available.
+- Failed to allocate a TFI
 No TFI available.
+No TFI available.
+- Failed to allocate a TFI
+No TFI available.
+No TFI available.
+- Failed to allocate a TFI