p9: Fix leak of waitqueue in request allocation path

If a T or R fcall cannot be allocated, the function returns an error
but neglects to free the wait queue that was successfully allocated.

If it comes through again a second time this wq will be overwritten
with a new allocation and the old allocation will be leaked.

Also, if the client is subsequently closed, the close path will
attempt to clean up these allocations, so set the req fields to
NULL to avoid duplicate free.

Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>