NFSD: Fault injection operations take a per-client forget function

The eventual goal is to forget state based on ip address, so it makes
sense to call this function in a for-each-client loop until the correct
amount of state is forgotten.  I also use this patch as an opportunity
to rename the forget function from "func()" to "forget()".

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>