Reduce duplication between MD parts of the Linuxulator

[dchagin]

Summary

In order to reduce duplication between MD parts of the Linuxulator
move bits that are MI out into the headers in compat/linux.
For that remove bogus _packed attribute from struct l_sockaddr
and use MI types for struct members.

And continue to move into the linux_common module a code that is
intended for both Linuxulator modules (both instruction set - 32 & 64 bit)
or for external modules like linsysfs or linprocfs.

To avoid header pollution introduce new sys/compat/linux_common.h header.

[emaste]

Overall looks good to me, a few comments inline. Minor comment - ideally we'd commit the verbatim code movement first in one commit followed by the new functionality (e.g. is_lo).

sys/compat/linux/linux.c

230

make is_eth and is_lo bool?

238

This line seems a bit awkward and style(9) prefers not using ! (in !strncmp) I think? What about just is_lo = len == 2 && strcmp(lxname, "lo") == 0;

272–280

Existing code but it seems we'd be better without any assumption Linux and FreeBSD flags are in the same bit, maybe something for a future change?

[dchagin]

Split the patch into two parts, modifying ifname_linux_to_bsd() will be next

[dchagin]

sys/compat/linux/linux.c

230

next review

238

next review

272–280

yes, I thought about it, I will fix this next