batman-adv: Add ap_isolation mesh/vlan genl configuration

The mesh interface can drop messages between clients to implement a
mesh-wide AP isolation.

The BATADV_CMD_SET_MESH/BATADV_CMD_GET_MESH and
BATADV_CMD_SET_VLAN/BATADV_CMD_GET_VLAN commands allow to set/get the
configuration of this feature using the BATADV_ATTR_AP_ISOLATION_ENABLED
attribute. Setting the u8 to zero will disable this feature and setting it
to something else is enabling this feature.

This feature also requires that skbuff which should be handled as isolated
are marked. The BATADV_CMD_SET_MESH/BATADV_CMD_GET_MESH commands allow to
set/get the mark/mask using the u32 attributes BATADV_ATTR_ISOLATION_MARK
and BATADV_ATTR_ISOLATION_MASK.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>