net/rds: fix WARNING in rds_conn_connect_if_down

stable inclusion
from stable-v4.19.310
commit 786854141057751bc08eb26f1b02e97c1631c8f4
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9L9M2
CVE: CVE-2024-27024

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=786854141057751bc08eb26f1b02e97c1631c8f4



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[ Upstream commit c055fc00c07be1f0df7375ab0036cebd1106ed38 ]

If connection isn't established yet, get_mr() will fail, trigger connection after
get_mr().

Fixes: 584a8279 ("RDS: RDMA: return appropriate error on rdma map failures")
Reported-and-tested-by:  <syzbot+d4faee732755bba9838e@syzkaller.appspotmail.com>
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Liu Jian <liujian56@huawei.com>