nfsd: fix uninitialised slot info when a request is retried

A recent patch moved the assignment of seq->maxslots from before the
test for a resent request (which ends with a goto) to after, resulting
in it not being run in that case.  This results in the server returning
bogus "high slot id" and "target high slot id" values.

The assignments to ->maxslots and ->target_maxslots need to be *after*
the out: label so that the correct values are returned in replies to
requests that are served from cache.

Fixes: 60aa6564 ("nfsd: allocate new session-based DRC slots on demand.")
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>