files/disable-tso: Refact script

Previous commit c98f8f55f745dc4d940a2c60fbe773d36fa57262 was not enough to fix
the problem.

The $LINE variable passed to vm_netlink and router_netlink doesn't use double
quotes so each column in $LINE is an argument and not a unique string.

7: qr-138be9c2-45: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
$1       $2                $3               $4  $5   $6     $7     $8     $9

Instead of getting the interface name in each function, the interface name is
filtered in ip_monitor and ethtool isn't applied to some interface like tap*
matching in the regex.

54: tap1c38b3fb-f7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
master qbr1c38b3fb-f7 state UNKNOWN mode DEFAULT qlen 500

ethool was applied to tap1c38b3fb-f7 because the regex matches with
qbr1c38b3fb-f7

Signed-off-by: Dimitri Savineau <dimitri.savineau@enovance.com>
Merge pull request #86 from dsavineau/refact-tso-script

files/disable-tso: Refact script