addons: bridge: add multi bridge support when bridge_set_static_mac_from_port=yes

addons: bridge: add multi bridge support when bridge_set_static_mac_from_port=yes

The policy bridge_set_static_mac_from_port was added to ifupdown2 back when we didn't
support a mix of traditional and vlan-aware bridges. The code wasn't revisited after
such config was allowed on the system.

how to repro:

- set bridge_set_static_mac_from_port=yes in module_globals of:
/var/lib/ifupdown2/policy.d/bridge.json

auto br1
iface br1
    bridge-vlan-aware no
    bridge-stp off
    bridge-ports swp1

auto bridge
iface bridge
    bridge-ports swp7
    bridge-vids 10
    bridge-vlan-aware yes

auto vlan10
iface vlan10
    address 192.168.0.20/32
    vlan-id 10
    vlan-raw-device bridge

br1 and bridge will share the same mac address (swp1's mac).

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>
Signed-off-by: Julien Fortin <jfortin@nvidia.com>