Increase performance of the squidclamav redirector.

To boost up the performance, now we trust the proxy cache.

I add some changes to the proxy.cgi to configure the proxy and the
squidclamav in the right way.

I also add a hook that allows us to generate a new configuration
if the cgi script will be launched from the shell.

Fixes #10367.
squidclamav: Update squidclamav.conf to use and trust the proxy cache.

If squidclamav is already installed, the configuration will be saved and updated during
the upgrade process.

Reference #10367.
squidclamav: Never use IPv6.

Squidclamav uses curl to resolve all kind of addresses which the system allow.
If the remote address is an IPv6 address, squidclamav hangs forever.

Nico Prenzel has found a solution to force the usage of IPv4 to prevent from this
issue.

Fixes #10376.
Cleanup in 30-network.menu.

* Removed entry for non existing upload.cgi.
* Fix indentation for several menu points.
dnsmasq: Add feature to forward domains to certain DNS servers.

Fixes #10369.
Merge remote-tracking branch 'stevee/dnsforward' into next
core71: add dnsforward to updater.
Merge remote-tracking branch 'stevee/proxy-squidclamav' into next

Conflicts:
	config/cfgroot/general-functions.pl
core71: add proxy-squidclam changes to updater.
misc-progs: fix typo in Makefile.
misc-progs: rootfile updates.