Create interfaces for each "port" in /etc/config/gluon

[lemoer]

This PR enables (migration-safe) role assignment for individual "lan" and "wan" interfaces. This is helpful especially on devices with multiple "lan" or "wan" interfaces (as they appear for devices with DSA support).

For interfaces in /lib/gluon/lan_ifname, we now create individual entries in /etc/config/gluon using a new introduced "/lan[0]", "/lan[1]", ... syntax. Before this PR, all interfaces were referenced as a single interface "/lan" in /etc/config/gluon.

The same is done for wan_ifname and single_ifname.

Migration strategy:

If new interfaces show up during gluon-reconfigure, the assigned roles of prior existing interfaces in the same category will be applied to the new interface.

(This PR is based on discussions in #2490)

[lemoer]

@NeoRaider What do you think?

[rotanid]

PR and commit contain "or" which should be "for"

[lemoer]

Thanks, fixed.

[lemoer]

As discussed above, I am closing this PR now.