slirp/arp: do not special-case bogus IP addresses

slirp/arp: do not special-case bogus IP addresses

Do not special-case addresses with zero host part, as we do not
necessarily know how big it is, and the guest can fake them anyway.
Silently avoid having 0.0.0.0 as a destination, however.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
[Edgar: Minor change to subject]
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>