The netipsec and pf tests have a number of common test functions. These used to be duplicated, but it makes more sense for them to re-use the common functions. PR: 236223
We now have a utility function to set pf rules in the jail. Use it whenever we need to set the pf rules in the test jail.
Introduce tests for the set-tos feature of pf. Teach pft_ping.py to send and verify ToS flags.