linux(4): Consolidate a FreeBSD interface names translation code

[dchagin]

Summary

We have some amount of interface names translation functions which are
differs by bugs implementation. Consolidates it in a one place.

MFC after: 3 days

[dchagin]

@jhibbits, I also reverted 52435989, as linprocfs code also needed to update

[jhibbits]

In D38714#881069, @dchagin wrote:

@jhibbits, I also reverted 52435989, as linprocfs code also needed to update

I just reverted that, so you can simplify your diff.

[dchagin]

Initialize ret to 0 for case when nothing is found

[dchagin]

Otimized, ethno calculated in callers to avoid one for over ifnets

[melifaro]

sys/compat/linux/linux.c

249

Nit: ‘const char *bsdname’. It would help to understand whar ‘len’ refers to

[dchagin]

ifnet_byindex, ifuint instead of handmade,
also use net ecoch in modified code, others later

[dchagin]

fix ifconf, btw, ifconf is no more used by glibc, replaced by netlink...

[dchagin]

ugh, fie net epoch in linprocfs donetroute, tested

[melifaro]

sys/compat/linux/linux.c

308

There can be more that one loopback interface, so I guess we need to rename only the first one (e.g. "lo0") and keep the rest intact.

sys/compat/linux/linux_ioctl.c

2169–2170

[dchagin]

fix lo -> lo0, loX -> loX translation