mount.nfs: Clean up after restructuring version/protocol negotiation

Fix up comments and function names to reflect the new version/protocol
negotiation scheme.  We can now remove a bunch of mount processing
that is specific to v2/v3, removing about 100 lines of logic from
stropts.c.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>