lib: Fix POSIX capabilities on SunOS platforms

lib: Fix POSIX capabilities on SunOS platforms

When using POSIX capabilities on SunOS the capabilities are too
restricitve resulting in quagga processes not being able to read their
own config files. Credit goes to Oracle where this patch was originally
authored and included in OpenSolaris.

lib/privs.c: Include additional capabilities, better checking of
    missing capabilities.

Fixes: #820
Acked-by: Greg Troxel <gdt@ir.bbn.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>