nvmet-tcp: fix lockdep complaint on nvmet_tcp_wq flush during queue teardown

stable inclusion
from stable-v5.10.138
commit 534e96302ad2cf24dfa6e6c2b18bc7c50ac16844
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60QFD

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=534e96302ad2cf24dfa6e6c2b18bc7c50ac16844



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[ Upstream commit 533d2e8b ]

We probably need nvmet_tcp_wq to have MEM_RECLAIM as we are
sending/receiving for the socket from works on this workqueue.
Also this eliminates lockdep complaints:
Reviewed-by: Wei Li <liwei391@huawei.com>