linux(4): Rename struct l_ifreq members names to avoid conflicts with FreeBSD

For now we are using mixed names to access struct ifreq members, some
of Linux (ifr_name, ifr_ifindex), others of FreeBSD. To avoid conflicts
switch to use FreeBSD names.

Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D38792