gprs: Do not put the subscr in gprs_subscr_delete

Currently gprs_subscr_delete implicitely calls subscr_put, which
makes the code more complex than necessary (additional subscr_get) in
a few places. It also makes it more difficult to see, whether get/put
are balanced within a function. In addition, the functions are not
named consistently (gprs_subscr_delete vs.
gprs_subscr_put_and_cancel).

This commit changes the semantics of gprs_subscr_delete and
indirectly of gprs_subscr_put_and_cancel to not call subscr_put on
their argument, but to leave that for the caller to do it
explicitely.

It renames gprs_subscr_put_and_cancel to gprs_subscr_cancel to
reflect that change in the name, too.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/gprs/gprs_sgsn.c b/openbsc/src/gprs/gprs_sgsn.c
index acf37a2..fdf4840 100644
--- a/openbsc/src/gprs/gprs_sgsn.c
+++ b/openbsc/src/gprs/gprs_sgsn.c
@@ -200,6 +200,7 @@
 		mm->subscr = NULL;
 		subscr->sgsn_data->mm = NULL;
 		gprs_subscr_delete(subscr);
+		subscr_put(subscr);
 	}
 
 	/* Free all PDP contexts */