Fix wrong gateway-address definition in instantiation-parameters for nst

Change-Id: I19ae0cae072a558f69d0facd8b1d78ec7d4b3541
Signed-off-by: Felipe Vicens <felipe.vicens@atos.net>
diff --git a/models/yang/instantiation-parameters.yang b/models/yang/instantiation-parameters.yang
index 0417bef..c5258ff 100644
--- a/models/yang/instantiation-parameters.yang
+++ b/models/yang/instantiation-parameters.yang
@@ -179,7 +179,7 @@
       type inet:ip-prefix;
     }
     leaf gateway-address {
-      type inet:ip-prefix;
+      type inet:ip-address;
     }
     list dns-server {
       key "address";