MFC r341172, r341270.
t4_clip.c had to be manually adjusted because Concurrency Kit is not
available in stable/11.

r341172:
Move CLIP table handling out of TOM and into the base driver.

• Store the clip table in 'struct adapter' instead of in the TOM softc.
• Init the clip table during attach and teardown during detach.
• While here, add a dev.<nexus>.<unit>.misc.clip sysctl to dump the CLIP table.

This does mean that we update the clip table even if TOE is not enabled,
but non-TOE things need the CLIP table anyway.

Reviewed by: np, Krishnamraju Eraparaju @ Chelsio
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D18010

r341270:
Make most of the CLIP code conditional on #ifdef INET6.

This fixes builds of kernels without INET6 such as LINT-NOINET6.

Reported by: arybchik
Reviewed by: np
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D18384