mgxe: Remove some fields from RX and TX ring struct

This packs RX and TX ring struct a little bit.
hammer2 - Add missing header file linkage

* Add vfs/hammer2 to the list of directories for /usr/obj softlinked
  headers.

Reported-by: swildner
hammer2 - Add missing header file linkage

* Add vfs/hammer2 to the BSD.include.dist mtree.

Reported-by: swildner