"Has PF_PACKET and SO_ATTACH_FILTER" does not imply "is Linux".

Solaris 11, for example, appears to support PF_PACKET sockets and socket
filters, presumably for for Linux compatibility, but it's not Linux and
doesn't have /usr/include/linux by default.
More "don't assume it's Linux if it has PF_PACKET and SO_ATTACH_FILTER".
Don't try to handle AF_PACKET on Solaris.
Note that we fixed Solaris 11 build problems.