Run bts_pch_timer_remove() on each entry of the BTS specific pch_timer
list, so we don't have a memory leak and so the timer doesn't
potentially fire for a deallocated BTS.
Fixes: d3c7591 ("Add counters: pcu.bts.N.pch.requests.timeout")
Change-Id: Ia5e33d1894408e93a51c452002ef2f5758808269
Implement T3113 for paging over PCH with default value of 7s (same as
T3113 in OsmoBSC). Increase the new counter on timeout.
Related: SYS#4878
Change-Id: I97475c3dbe2cf00b9cbfec39e93a3c65cb7f749f