gbproxy: Remove SGSN-side BVC after sending BVC-BLOCK

If we keep the bvc around the SGSN could send a BVC-RESET which the
gbproxy would ACK. This will reestablish the BVC only between the gbproxy and
SGSN which can lead to all sorts of issues.

With this patch the gbproxy will respond with a BVC-STATUS cause BVCI
unknown.

Related: SYS#5628
Fixes: OS#5236
Change-Id: Ib14be6425a81b43353708b2708f79e035e501079

src/gb_proxy.c

@@ -1627,6 +1627,7 @@ void gprs_ns_prim_status_cb(struct gbproxy_config *cfg, struct osmo_gprs_ns2_pri
 					/* Block BVC, indicate BSS equipment failure */
 					uint8_t cause = BSSGP_CAUSE_EQUIP_FAIL;
 					osmo_fsm_inst_dispatch(sgsn_bvc->fi, BSSGP_BVCFSM_E_REQ_BLOCK, &cause);
+					gbproxy_bvc_free(sgsn_bvc);
 				}
 			}