constify arg in addr_is_any()

Change-Id: Ie8cb750d2e265bae48bbfa8ea1d88f3e316879ed
diff --git a/src/libosmo-mgcp/mgcp_network.c b/src/libosmo-mgcp/mgcp_network.c
index 1b7c3bd..1014bf2 100644
--- a/src/libosmo-mgcp/mgcp_network.c
+++ b/src/libosmo-mgcp/mgcp_network.c
@@ -77,7 +77,8 @@
 
 static int rx_rtp(struct msgb *msg);
 
-static bool addr_is_any(struct osmo_sockaddr *osa) {
+static bool addr_is_any(const struct osmo_sockaddr *osa)
+{
 	if (osa->u.sa.sa_family == AF_INET6) {
 		struct in6_addr ip6_any = IN6ADDR_ANY_INIT;
 		return memcmp(&osa->u.sin6.sin6_addr,