pf: fix mem leaks upon vnet destroy

Add missing cleanup actions:

• remove user defined anchor rulesets
• remove user defined ether anchor rulesets
• remove tables linked to user defined anchors
• deal with wildcard anchor peculiarities to get them removed correctly

PR: 274310
Reviewed by: kp
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D42747

(cherry picked from commit 0626d30e41cba64b41667314c3a4f7611f0eb685)