(traffic shaper) add flush all and reload action, closes https://github.com/opnsense/core/issues/1297

Way better fix for the squid file transition.  Does not require
a manual restart anymore.

edns flag was added in 2014, but it could never be set.
Remove buffer size override along with it to further
simplify the situation.

See: https://github.com/pfsense/pfsense/commit/3b95d9e

People who use these know what they are doing, for everybody else
this is just plain confusing.

The regdhcp conditional option never really worked in the first place.
Dhcplease registration is controlled by regdhcp and regdhcpstatic
elsewhere already and we always need to include this file.

PR: https://forum.opnsense.org/index.php?topic=4041

Right now, kern.hz is 1000 by default, and, more surprisingly,
net.inet.tcp.rexmit_min is 30 in FreeBSD too...

when ipfw isn't configured, the service won't (re)start throwing an error, use of onestart instead of start fixes this. closes https://github.com/opnsense/core/issues/1292

Save doesn't trigger in dialog yet, though.