Cross reference cdce(4), ipheth(4) and urndis(4) from each other.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272107 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
add missing file

Submitted by:	Daniel Peyrolon
MFC after:	3 days


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272108 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f