gprs_ns2_sns: Fix memory leak when creating ip[46]_local arrays

Prior to this patch, we would unconditionally allocate new memory
for the local SNS IP endpoints.   This results in a memory leak
on every SNS-SIZE procedure.

Let's move to talloc_realloc() which recycles any previously allocated
memory.

Change-Id: I12cb670e087c6d6190f3f5bf8483ea62008ae06f
diff --git a/src/gb/gprs_ns2_sns.c b/src/gb/gprs_ns2_sns.c
index b07f010..144ab21 100644
--- a/src/gb/gprs_ns2_sns.c
+++ b/src/gb/gprs_ns2_sns.c
@@ -811,7 +811,7 @@
 
 	switch (gss->ip) {
 	case IPv4:
-		ip4_elems = talloc_zero_size(fi, sizeof(struct gprs_ns_ie_ip4_elem) * count);
+		ip4_elems = talloc_realloc(fi, gss->ip4_local, struct gprs_ns_ie_ip4_elem, count);
 		if (!ip4_elems)
 			return;
 
@@ -846,7 +846,7 @@
 		break;
 	case IPv6:
 		/* IPv6 */
-		ip6_elems = talloc_zero_size(fi, sizeof(struct gprs_ns_ie_ip6_elem) * count);
+		ip6_elems = talloc_realloc(fi, gss->ip6_local, struct gprs_ns_ie_ip6_elem, count);
 		if (!ip6_elems)
 			return;
 
@@ -925,7 +925,6 @@
 		gss->sns_nsvc->sns_only = true;
 	}
 
-
 	if (gss->num_max_ip4_remote > 0)
 		ns2_tx_sns_size(gss->sns_nsvc, true, gss->num_max_nsvcs, gss->num_ip4_local, -1);
 	else