linux(4): Migrate to IfAPI

[dchagin]

Summary

Migrate linux and linprocfs to use the IfAPI interfaces instead of
direct ifnet accesses.

[jhibbits]

sys/compat/linprocfs/linprocfs.c

1492

Just style, do we need the spaces here?

[dchagin]

ah, casts and sizeof's are not followed by a space. so, whitespaces are gone
Thank you!

[dchagin]

ugh, bug found in ifconf code,
linux_ifconf_ifaddr_cb2() should return 1 as if_foreach_addr_type()
counts from 0, so addrs always is 0 and linux_ifconf_ifnet_cb2() always
adds cruft entries with address 0. Linux skips interfaces not running and without addresses .