sockets: factor out create_fast_reuse_socket

Another refactoring step to prepare for fixing the problem
exposed with the test-listen test in the previous commit

Signed-off-by: Knut Omang <knut.omang@oracle.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
