Report error if unable to bind to any socket

Report error if unable to bind to any socket

When setting up a server socket, we must skip EADDRINUSE errors
from bind, since the IPv6 socket bind may have already bound to
the IPv4 socket too. If we don't manage to bind to any sockets
at all though, we should then report the EADDRINUSE error as
normal.

This fixes the case where libvirtd would not exit if some other
program was listening on its TCP/TLS ports.

* src/rpc/virnetsocket.c: Report EADDRINUSE