[FS#944] firewall3 isn't holding iptables lock

[LEDE Bugs]

The following task has a new comment added:

FS#944 - firewall3 isn't holding iptables lock
User who did this - Jo-Philipp Wich (jow-)

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The current iptables release is not supporting `-w` for iptables-restore and the mentioned commit is not easily backportable.

Unless the current iptables release is not implementing `-w` properly, we cannot support this feature. Consider protecting your other racing code with a call to "lock /var/run/fw3.lock".
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=944#comment3187