tbf: Maintain the number of TBF per PDCH

Currently the PDCH object do not know anything about the TBFs using
them. To make the slot allocation load dependant, at least some
numbers are required.

This commit adds TBF counters (one per direction) and the related methods
attach_tbf, detach_tbf, and num_tbfs to gprs_rlcmac_pdch.

Sponsored-by: On-Waves ehf
5 files changed