scripts: Support monitoring of interestingly named VLANs on bonds

scripts: Support monitoring of interestingly named VLANs on bonds

VLAN interfaces on bonds with a name other than <iface>.<id>@<iface>
are not currently supported.  That is, where the VLAN name isn't based
on the underlying bond name.  Such VLAN interfaces can be created with
the "ip link" command, as opposed to the "vconfig" command, or by
renaming a VLAN interface.

This is improved by determining the underlying interface name for a
VLAN from the output of "ip link".

No serious attempt is made to support VLANs with '@' in their name,
although this seems to be legal.  Why would you do that?

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
(Imported from commit bc71251433ce618c95c674d7cbe75b01a94adad9)