vlan: Add GVRP support

Add GVRP support for dynamically registering VLANs with switches.

By default GVRP is disabled because we only support the applicant-only
participant model, which means it should not be enabled on vlans that
are members of a bridge. Since there is currently no way to cleanly
determine that, the user is responsible for enabling it.

The code is pretty small and low impact, its wrapped in a config
option though because it depends on the GARP implementation and
the STP core.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/8021q/vlan_netlink.c b/net/8021q/vlan_netlink.c
index fd7cb19..e9c91dc 100644
--- a/net/8021q/vlan_netlink.c
+++ b/net/8021q/vlan_netlink.c
@@ -59,7 +59,8 @@
 	}
 	if (data[IFLA_VLAN_FLAGS]) {
 		flags = nla_data(data[IFLA_VLAN_FLAGS]);
-		if ((flags->flags & flags->mask) & ~VLAN_FLAG_REORDER_HDR)
+		if ((flags->flags & flags->mask) &
+		    ~(VLAN_FLAG_REORDER_HDR | VLAN_FLAG_GVRP))
 			return -EINVAL;
 	}