gprs_ns2: const the return value of gprs_ns2_ip_vc_sockaddr / gprs_ns2_ip_bind_sockaddr

The sockaddr should not be changed.
free and create the bind/nsvc if the address should be changed.

Change-Id: I371ac2361b569e36722b02fc9cd82ec8da2fa9e3
diff --git a/include/osmocom/gprs/gprs_ns2.h b/include/osmocom/gprs/gprs_ns2.h
index 7531530..a3edc63 100644
--- a/include/osmocom/gprs/gprs_ns2.h
+++ b/include/osmocom/gprs/gprs_ns2.h
@@ -139,8 +139,8 @@
 			    const struct osmo_sockaddr *remote,
 			    uint16_t nsei);
 
-struct osmo_sockaddr *gprs_ns2_ip_vc_sockaddr(struct gprs_ns2_vc *nsvc);
-struct osmo_sockaddr *gprs_ns2_ip_bind_sockaddr(struct gprs_ns2_vc_bind *bind);
+const struct osmo_sockaddr *gprs_ns2_ip_vc_sockaddr(struct gprs_ns2_vc *nsvc);
+const struct osmo_sockaddr *gprs_ns2_ip_bind_sockaddr(struct gprs_ns2_vc_bind *bind);
 int gprs_ns2_is_ip_bind(struct gprs_ns2_vc_bind *bind);
 int gprs_ns2_ip_bind_set_dscp(struct gprs_ns2_vc_bind *bind, int dscp);
 struct gprs_ns2_vc *gprs_ns2_nsvc_by_sockaddr_bind(