ip: reassembly - return correct value

If already enabled, return 0 to indicate success.

Type: fix
Change-Id: I4a182e14df9b05698ad93d596a97c46a020fd54b
Signed-off-by: Klement Sekera <klement.sekera@gmail.com>
diff --git a/src/vnet/ip/reass/ip4_full_reass.c b/src/vnet/ip/reass/ip4_full_reass.c
index 7f0b8d9..bab7d47 100644
--- a/src/vnet/ip/reass/ip4_full_reass.c
+++ b/src/vnet/ip/reass/ip4_full_reass.c
@@ -2059,7 +2059,7 @@
 					    "ip4-full-reassembly-feature",
 					    sw_if_index, 0, 0, 0);
     }
-  return -1;
+  return 0;
 }
 
 void