bts: delete pch_timer list in destructor

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
diff --git a/src/bts.cpp b/src/bts.cpp
index a40e071..daa8ee1 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -32,6 +32,7 @@
 #include <pdch.h>
 #include <gprs_ms_storage.h>
 #include <sba.h>
+#include <bts_pch_timer.h>
 
 extern "C" {
 	#include <osmocom/core/talloc.h>
@@ -230,6 +231,8 @@
 		bts->app_info = NULL;
 	}
 
+	bts_pch_timer_stop_all(bts);
+
 	llist_del(&bts->list);
 	return 0;
 }