add support for network trunks

add support for network trunks

This add support for net trunks vlan filtering
for ovs and linux vlan-aware bridge

Can be mixed with current "tag" option

examples:
----------

allow only 802.1Q packets with vlanid 2,3,4 :

netx: .....,trunks=2,3,4

allow only 802.1Q packets with vlanid 2,3,4 and tag non-802.1Q packets to vlanid 5 :

netx: tag=5,trunks=2,3,4

tag non-802.1Q packets to vlanid 5

netx: tag=5
Signed-off-by: Alexandre Derumier <aderumier@odiso.com>