Adding waiting (-w) in iptables for wg-iptables service

At one point I overloaded the server and Wireguard was not working on it. I began to understand and found out that the wg-iptables service did not start. The logs were:

May 19 17:50:27 server.domain iptables[714]: Another app is currently holding the xtables lock. Perhaps you want to use the -w option?
May 19 17:50:27 server.domain systemd[1]: wg-iptables.service: Main process exited, code=exited, status=4/NOPERMISSION
May 19 17:50:27 server.domain systemd[1]: wg-iptables.service: Failed with result 'exit-code'.
May 19 17:50:27 server.domain systemd[1]: Failed to start wg-iptables.service.

Then I started googling this problem and found out that the problem is that your startup commands do not specify to wait in case of blocking. This patch fixes the problem.

@Nyr I would love to see that merged!