solaris: preliminary support

Basic functionalities are present. However, the interface support is
very poor. There is no way to detect bridges, VLAN and
aggregates. There is no MAC/PHY support. There is no detection of
wireless devices.

The code to detect IP forwarding is here but does not work inside the
chroot.
solaris: assume that IP forwarding is disabled

We don't know how to detect that while in the chroot.
solaris: less intrusive way to get CMSG_* macros

The use of _XOPEN_SOURCE breaks most BSD.
NEWS: add a word about Solaris support