network-legacy/net-genrules.sh: use $name instead of $env{INTERFACE}

network-legacy/net-genrules.sh: use $name instead of $env{INTERFACE}

The original behavior of $env{INTERFACE} was undocumented and changed in
the recent udev versions, breaking the ability to bring up networking
reliably. Switching to $name directive should fix this issue.

Related links:
 - systemd/systemd#12700 (udev PR)
 - systemd/systemd#12291 (related udev issue)
 - systemd/systemd#14935 (this issue, udev side)
 - #732 (this issue, dracut side)

Fixes: #732