It is actually possible to have if_t a typedef to non-void type,
and keep both converted to drvapi and non-converted drivers
compilable.

o Make if_t typedef to struct ifnet *.
o Remove shim functions.

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git-svn-id: svn+ssh://svn.freebsd.org/base/head@270876 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f