MAINT: Fix AF_LINK warnings through systemd

cd068fe added `RestrictAddressFamilies=~AF_PACKET AF_NETLINK`

which was sourced from https://github.com/archlinux/svntogit-community/blob/ba167269f8336659313d589dea65642b4eae4f85/trunk/murmur.service
where it was added in archlinux/svntogit-community@d609d47
described as "hardening" without further reasoning or information.

The disallow of `AF_LINK` leads to continuous spamming of `Address family not supported by protocol` in the systlog. Dropping this resolves that.

Resolves #6180

auxiliary_files/config_files/mumble-server.service.in

@@ -22,7 +22,7 @@ ProtectKernelLogs=yes
 ProtectKernelModules=yes
 ProtectKernelTunables=yes
 ProtectSystem=full
-RestrictAddressFamilies=~AF_PACKET AF_NETLINK
+RestrictAddressFamilies=~AF_PACKET
 RestrictNamespaces=yes
 RestrictSUIDSGID=yes
 RestrictRealtime=yes