virsocket: Don't preserve errno in virSocketRecvFD()

virsocket: Don't preserve errno in virSocketRecvFD()

When setting O_CLOEXEC flag on received FD fails the FD is closed
using VIR_FORCE_CLOSE(). But the call is wrapped in errno save
which is not necessary because VIR_FORCE_CLOSE() preserves  errno
value.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>