IPS (netmap) support ixl driver (and possibly others)

[AdSchellevis]

Since FreeBSD 12.x quite some drivers have been converted to iflib (https://www.freebsd.org/cgi/man.cgi?query=iflib), including the intel ixl one.

Since netmap on ixl still has issues on OPNsense 20.1, we decided to wait for 20.7 for further testing and analysis.

Out of the box more hardware support seems to be enabled for vlan's, which doesn't play nice with netmap (leading to loss of data).

ixl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=8500b8<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,VLAN_HWFILTER,VLAN_HWTSO>

Since netmap requires hardware support to be disabled, we should disable all hardware switches for proper functionality.

• change "disablevlanhwfilter" to disabled in our default configuration, the "leave default" option was originally added for other ix[l] stability issues when changing the option. (2fc3baa)
• when disablevlanhwfilter equals 1, make sure vlanhwcsum, vlanhwfilter, vlanhwtso, vlanhwtag are all disabled (doesn't seem to be the case now)
• set hw.ixl.enable_head_writeback defaults to 0.

[mimugmail]

Yes, it should be disabled, I also pinged SunnyValley about this in their testing:
https://forum.opnsense.org/index.php?topic=17656.msg80170#msg80170

Hopefully next week I'm in the office and can test 20.7 with some ix drivers too.

[AdSchellevis]

with those disabled, it looks stable on my machine (running iperf for a couple of minutes now). I'll make sure to let Murat know as well.

[mimugmail]

Great, maybe directly here:
https://docs.google.com/spreadsheets/d/1RVj8K3XOzWi-Bkjq6hUxWudu7Cxd8FFTqjLiBMzZWEM/edit?ts=5ee51424#gid=0

A list of SunnyValley for checking compatibility.

[L1ghtn1ng]

I have been doing testing with sunnyvalley on this