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.c b/src/gb/gprs_ns2.c
index 57a08d1..835c22a 100644
--- a/src/gb/gprs_ns2.c
+++ b/src/gb/gprs_ns2.c
@@ -824,7 +824,7 @@
  *  \param[in] nse NS Entity in which to search
  *  \param[in] sockaddr socket address to search for
  *  \return NS-VC matching sockaddr; NULL if none found */
-struct gprs_ns2_vc *gprs_ns2_nsvc_by_sockaddr(struct gprs_ns2_nse *nse,
+struct gprs_ns2_vc *gprs_ns2_nsvc_by_sockaddr_nse(struct gprs_ns2_nse *nse,
 					      struct osmo_sockaddr *sockaddr)
 {
 	struct gprs_ns2_vc *nsvc;