fff-network: Have WAN sysctl commands executing after global ones

On layer3 variant ("gateway firmware"), 60-fff-gateway.conf
changes "forwarding" for all interfaces, overwriting the
changes from 51-fff-network-$iface.conf.

By putting the WAN-specific commands after 60-fff-gateway.conf
this patch should provide the correct device-specific value
for WAN interface now.

Signed-off-by: Robert Langhammer <rlanghammer@web.de>
Reviewed-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
[Rephrased commit title and added message]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>