make interface name regex less strict to support systemd 197

the stupidity coming from systemd bites again. they've implemented
"persistent" network naming, which is persistent (like they already
are), but not predictable. for example, my desktop LAN connection
changes from "eth0" to "enp3s0f0". So simple!
on conclusion, there are now too many possible combinations of valid
interface names that it's no longer viable to sanity check the values
provided.