Mechanically convert to if_inc_counter().


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272226 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Convert driver to if_get_counter method.

Submitted by:	rstone
Reviewed by:	Eric Joyner <ricera10 gmail.com>


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272227 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f