Redmine #6590: Add leaner version of Solaris MAC address detection.

Also made sure that Solaris does not select the getifaddrs version,
since although the function is available, it cannot actually be used
to get the MAC address.

And removed a suppressed failure for Windows which is not correct
anymore.
Redmine #6590: Revert "add implementation of getifaddrs for solaris"

This reverts commit debbe3e770dd1ff8e2211ba2c2d3e5d2cbc36739.

Conflicts:

	libpromises/Makefile.am
	libpromises/solaris_ifaddrs.c
	libpromises/solaris_ifaddrs.h
	libpromises/unix.c