nfsd: re-order client tracking method selection

The new order is first nfsdcld, then the UMH upcall, and finally the
legacy tracking method.  Added some printk's to the tracking
initialization functions so it's clear which tracking method was
ultimately selected.

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>