gre: fix feature.yaml error

vnet/gre/FEATURE.yaml does not conform with the JSON schema definition.
This bug should no longer happen with the patch that ensures
validation is run as part of checkstyle.

Signed-off-by: Ole Troan <ot@cisco.com>
Type: fix
Change-Id: I25bf8d2a442bf7ccdbf693b031a7a383444dfee3
diff --git a/src/vnet/gre/FEATURE.yaml b/src/vnet/gre/FEATURE.yaml
index a794dac..5e0e77c 100644
--- a/src/vnet/gre/FEATURE.yaml
+++ b/src/vnet/gre/FEATURE.yaml
@@ -6,8 +6,8 @@
   - Encap/Decap flags to control the copying of DSCP, ECN, DF from overlay to
     underlay and vice-versa.
   - L2 tunnels
-  - NOT supported: keys.
-
+missing:
+  - GRE keys
 description: "GRE"
 state: production
 properties: [API, CLI, MULTITHREAD]