P2P: Use alternative way of starting dnsmasq if needed

P2P: Use alternative way of starting dnsmasq if needed

Some other dnsmasq users (like libvirt) seem to be binding the DHCP
server to all interfaces which prevents the previously used mechanism
here from working (bind on the DHCP socket fails). If a failure is
noticed, try to start dnsmasq with -z option to avoid that.