cbch: Fix dangling cur_msg leading to double-free in bts_cbch_reset()
cbch: Fix dangling cur_msg leading to double-free in bts_cbch_reset()

If a new default message is installed via RSL, and the old default
message is currently being transmitted, we must set cur_msg to NULL.

The old default message must be talloc_free()d unconditionally whenever
a new default message is being set.

We can do that by using the TALLOC_FREE macro.

Change-Id: Id32c2074b61cd1f09957b9d1558ffb3a7691a8e0
Related: OS#5325

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts