tbf: Add GprsMs* argument to update() and use it in reuse_tbf

Since set_ms() is caled on the new DL TBF, the old DL TBF loses the
reference to the MS object. This will lead to a segfault, when
update() is called in reuse_tbf().

This commit adds an optional GprsMs* parameter to update() and uses it
for the slot allocation.

This fixes a TbfTest crash that would otherwise occur after applying
the next commit.

Sponsored-by: On-Waves ehf
3 files changed