aliases: Add support to assign aliases to multiple RED interfaces

aliases: Add support to assign aliases to multiple RED interfaces

This is a little patch which will extend the aliases page to offer an
interface selection if there are more than one RED interfaces.

This is a little hack to make configuration easier for users who have
manually set up more than one RED interface (e.g. for load balancing or
fail-over) and want to use the UI to configure firewall rules.

As a little benefit on the side, I had to rewrite setaliases.c to use
ip(8) instead of ifconfig(8).

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
Acked-by: Peter Müller <peter.mueller@ipfire.org>