pf: Handle if_groups with the same name as interfaces

[kp]

Summary

pf allows network interfaces and groups to be used interchangeably. They don't
share a namespace so it's possible for an interface and a group to have the same
name.

If that happens we recurse infinitely in pfi_kif_update() because the pfi_kif is
both an interface and a group. That means that the kif is a member of itself.

Simply checking that we're not calling pfi_kif_update() on the current pfi_kif
fixes the panic.

PR: 127042, 202178

[eri]

I do not think this is the root cause for this, it just hides another issue.
I think that the result of RB_INSERT should be checked when a group/iface is created should be tested.
If that returns NULL the result should be null.

To me it is not good to have this weirdness in the configuration and nevertheless allow that.

[kp]

I'll post a patch with an alternative approach: change the network stack to put ifgroup and interface names in the same namespace.

[kp]

Alternate approach in https://reviews.freebsd.org/D7528