SUNRPC: remove scheduling boost for "SWAPPER" tasks.

SUNRPC: remove scheduling boost for "SWAPPER" tasks.

BugLink: https://bugs.launchpad.net/bugs/1969107
[ Upstream commit a80a8461868905823609be97f91776a26befe839 ]

Currently, tasks marked as "swapper" tasks get put to the front of
non-priority rpc_queues, and are sorted earlier than non-swapper tasks on
the transport's ->xmit_queue.

This is pointless as currently *all* tasks for a mount that has swap
enabled on *any* file are marked as "swapper" tasks.  So the net result
is that the non-priority rpc_queues are reverse-ordered (LIFO).

This scheduling boost is not necessary to avoid deadlocks, and hurts
fairness, so remove it.  If there were a need to expedite some requests,
the tk_priority mechanism is a more appropriate tool.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit a553864050944656c6225056d3704500fbbf6f38)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>