gprs_ns2: gprs_ns2_ip_vc_remote() the nsvc can be also const

Change-Id: Ia000f535f18f21b41038f2ce7721f0fb59f6a093
diff --git a/src/gb/gprs_ns2_udp.c b/src/gb/gprs_ns2_udp.c
index a3e9da6..d41c492 100644
--- a/src/gb/gprs_ns2_udp.c
+++ b/src/gb/gprs_ns2_udp.c
@@ -413,7 +413,7 @@
 /*! Return the socket address of the remote peer of a NS-VC.
  *  \param[in] nsvc NS-VC whose remote peer we want to know
  *  \return address of the remote peer; NULL in case of error */
-const struct osmo_sockaddr *gprs_ns2_ip_vc_remote(struct gprs_ns2_vc *nsvc)
+const struct osmo_sockaddr *gprs_ns2_ip_vc_remote(const struct gprs_ns2_vc *nsvc)
 {
 	struct priv_vc *priv;