In bhyve's fbuf emulation improve the overall "usage" message and
for the vga option, rather than printing the entire option string,
only print vga (as we do for everything else).

Allow the bhyve VNC server to listen on IPv6 for incoming connections.

Alternatively to IPv4 address:port this will allow to listen on IPv6
link-local (incl. scope), a specific address, or ::.  Addresses have
to be given in RFC2732 format so that [::]:port parsing will work.

This patch also starts to introduce WITH_INET/INET6_SUPPORT to bhyve.

Submitted by:	Dave Rush (northwoodlogic.free gmail.com) (original)
Reviewed by:	Dave Rush (updated verison)