dpaa2: ni: add more stats and link information

In addition to the locally generated statistics counters, dpaa2 ni
provides a larger set of counters than we currently export via
sysctl. Add (most of) the missing counters and descriptions.
Around Page 3/4 there are some things left to do if we want.
Also the manual was not clear on the descriptions of 3/0 and 3/1.

The second half of the change adds another sysctl note which exports
the link-state, speed, and capabilities set as a text-blob. This is
especially interesting in case the "ni" stops passing packets.
From what I have found in that case the (internal) link state of the
ni goes DOWN but we do not see an interrupt for a link-state change.

Being able to diagnose the state helps to (manually) fix it for now
by changing the media status to 10BaseT or none and then back to auto.
That usually brings the internal link state back UP.

PR: 279352
Reviewed by: dsl, tuexen
Differential Revision: https://reviews.freebsd.org/D55321

(cherry picked from commit c8cd633d78d04ff535960002ac9d1ab20f74b201)