delete_bifcs.cgi and save_bifc.cgi only called deactivate_interface()
which brings the link down but never removes the virtual device.
Added destroy_interface_device() that does ip link delete for these.
Also had to add bridge creation (ip link add type bridge) because unlike
bond (81d44f8) and VLAN (7761066) that was still missing.
Other fixes in this commit:
debian-linux-lib.pl: bonding opts were single-element arrays causing
trailing spaces in /etc/network/interfaces on every save.
linux-lib.pl: ip link set up/down was gated behind a
bond/vlan/no-ifconfig check but ip addr add runs unconditionally - so
interfaces got an IP but stayed DOWN. Dropped the unnecessary guard.
Mike Steinmetz
b050127ded