addons: bridge: if device exists - check if device is really a bridge

addons: bridge: if device exists - check if device is really a bridge

[18:43:47] root:~ # ip link show swp3
5: swp3: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether 08:00:27:bc:04:3c brd ff:ff:ff:ff:ff:ff
[18:43:48] root:~ #
[18:43:49] root:~ #
[18:43:50] root:~ # cat /etc/network/interfaces
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

auto swp3
iface swp3
	bridge-vlan-aware yes
[18:43:50] root:~ #
[18:43:51] root:~ #
[18:43:51] root:~ # ifup -a
warning: swp3: error getting dependent interfaces (misconfiguration of bridge attribute(s) on existing non-bridge interface (swp3))
[18:43:56] root:~ # echo $?
1
[18:43:58] root:~ #

Reviewed-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>