alloc: Load balancing for algo A

Currently only the first enabled PDCH will be used. Beside the
throughput this will also limit the number of TBFs:

  - number of UL TBFs <= 7
  - number of DL TBFs <= 32

This commit changes the allocation algorithm to use the PDCH with the
least number of attached TBFs. This will improve the troughput in
both directions and the UL limits:

  - number of UL TBFs <= min(32, N_PDCH * 7) UL TBFs

Ticket: #1794
Sponsored-by: On-Waves ehf
5 files changed