gb_proxy_peer: Add Function to get gbproxy cell by cell id

Change-Id: I3403736eed9d6819634c26db0b90393ac6f4416a
Related: SYS#5103
diff --git a/include/osmocom/sgsn/gb_proxy.h b/include/osmocom/sgsn/gb_proxy.h
index 269b851..96b2bcc 100644
--- a/include/osmocom/sgsn/gb_proxy.h
+++ b/include/osmocom/sgsn/gb_proxy.h
@@ -270,6 +270,7 @@
 
 struct gbproxy_cell *gbproxy_cell_alloc(struct gbproxy_config *cfg, uint16_t bvci);
 struct gbproxy_cell *gbproxy_cell_by_bvci(struct gbproxy_config *cfg, uint16_t bvci);
+struct gbproxy_cell *gbproxy_cell_by_cellid(struct gbproxy_config *cfg, const struct gprs_ra_id *raid, uint16_t cid);
 void gbproxy_cell_free(struct gbproxy_cell *cell);
 bool gbproxy_cell_add_sgsn_bvc(struct gbproxy_cell *cell, struct gbproxy_bvc *bvc);