ms_need_dl_tbf(): Fix state checks and document function

A new state TBF_ST_WAIT_REUSE_TFI was added lately in dl_tbf_fsm, which
allows differentiating the time where the MS is listening on PACCH
after having sent last DL ACK/NACK, and time where it should already be
in idle mode.
In the former, the ms_need_dl_tbf() should return false since the MS is
still ongoing in packet-active mode (and new data incoming from SGSN
will trigger new DL TBF assignment over PACCH as needed), while in the
later we want to start a new PCH assignment.

Fixes: 40a297f3b0c8e1670d46a4974750dd3335bc7885
Change-Id: I96f311480d036859511c6ba825ccd36bdc71190b
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M src/gprs_ms.h
1 file changed, 41 insertions(+), 3 deletions(-)