gprs_ns_vty: return success for disabled FR/GRE

Do not return a warning and therefore fail parsing the config when the
"encapsulation framerelay-gre local-ip" command is used and FR/GRE is
disabled. Having this in the config does no harm and allows keeping the
same config if it is enabled later.

This fixes the currently failing vty tests for osmo-sgsn.

Fixes: a0c8195ad37292ab800a6c777fc28383995b4b64 ("vty: Return error if cmd returns CMD_WARNING while reading cfg file")
Change-Id: Ic225232fbfca49ba868427eaf898e1f6e34e1ca8
diff --git a/src/gb/gprs_ns_vty.c b/src/gb/gprs_ns_vty.c
index 4a90436..9cffb71 100644
--- a/src/gb/gprs_ns_vty.c
+++ b/src/gb/gprs_ns_vty.c
@@ -508,10 +508,6 @@
 {
 	struct in_addr ia;
 
-	if (!vty_nsi->frgre.enabled) {
-		vty_out(vty, "FR/GRE is not enabled%s", VTY_NEWLINE);
-		return CMD_WARNING;
-	}
 	inet_aton(argv[0], &ia);
 	vty_nsi->frgre.local_ip = osmo_ntohl(ia.s_addr);