fix segfault upon release paging on BSSMAP Reset: init llist

Initialize the llist head gsm_bts->paging.pending_requests at the time gsm_bts
is allocated, not only at paging_init_if_needed().

The gsm_bts->paging sub-struct is invalid as long as gsm_bts->paging.bts
doesn't point back to bts. Hence the recently added iteration of
gsm_bts->paging.pending_requests should have checked whether bts is NULL. The
llist_head pending_requests is not initialized unless paging_init_if_needed()
has been called (and paging.bts is hence set). However, this fix is a safer way
to prevent errors like this in general.

The segfault was introduced by d382bf63e2b7e28fe41c5310c26fe584f0356897 /
If3f53d3bb66ad2dc02db823cb813590c6b59c700

Related: OS#2747
Change-Id: Idfafac4e2c0e0a241a62aecbbdc22be71febf840
2 files changed