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>

include/linux/if_vlan.h

@@ -402,6 +402,7 @@ enum vlan_ioctl_cmds {
 
 enum vlan_flags {
 	VLAN_FLAG_REORDER_HDR	= 0x1,
+	VLAN_FLAG_GVRP		= 0x2,
 };
 
 enum vlan_name_types {