Add set ToS test for ipfw and pf

[ahsanb]

Summary

Add the set ToS test for ipfw and pf. This test tests the following:

• The firewall is able to set the tos bits
• The firewall is able to set the DSCP bits when EN bits is already set and the EN bits remains unchanged.
• The firewall is able to drop the packets based on ToS value

Note: This diff must be applied after applying D21276

[thj]

tests/sys/netpfil/common/tos.sh

64 ↗

(On Diff #60943)

Can you wrap this comment and the two below so that there lines don't wrap? This one might be fine, but the one below is probably too long

[ahsanb]

• wrap the comments