ns2: refactor nsvc_by_ functions

gprs_ns2_nsvc_by_sockaddr_nsei is doing the lookup within a NSE.
gprs_ns2_nsvc_by_sockaddr_bind is doing the lookup within a bind.
Make both function look similiar and take similiar arguments.

Change-Id: Ia499fc279013668abe7348e578a0768f7d16faf9
diff --git a/src/gb/gprs_ns2_sns.c b/src/gb/gprs_ns2_sns.c
index 812200d..753ac4d 100644
--- a/src/gb/gprs_ns2_sns.c
+++ b/src/gb/gprs_ns2_sns.c
@@ -179,7 +179,7 @@
 	sa.u.sin.sin_port = ip4->udp_port;
 	sa.u.sin.sin_family = AF_INET;
 
-	return gprs_ns2_nsvc_by_sockaddr(nse, &sa);
+	return gprs_ns2_nsvc_by_sockaddr_nse(nse, &sa);
 }
 
 static struct gprs_ns2_vc *nsvc_by_ip6_elem(struct gprs_ns2_nse *nse,
@@ -191,7 +191,7 @@
 	sa.u.sin6.sin6_port = ip6->udp_port;
 	sa.u.sin6.sin6_family = AF_INET;
 
-	return gprs_ns2_nsvc_by_sockaddr(nse, &sa);
+	return gprs_ns2_nsvc_by_sockaddr_nse(nse, &sa);
 }
 
 /*! called when a nsvc is beeing freed */