rds: tcp: must use spin_lock_irq* and not spin_lock_bh with rds_tcp_conn_lock

rds_tcp_connection allocation/free management has the potential to be
called from __rds_conn_create after IRQs have been disabled, so
spin_[un]lock_bh cannot be used with rds_tcp_conn_lock.

Bottom-halves that need to synchronize for critical sections protected
by rds_tcp_conn_lock should instead use rds_destroy_pending() correctly.

Reported-by:  <syzbot+c68e51bb5e699d3f8d91@syzkaller.appspotmail.com>
Fixes: ebeeb1ad

 ("rds: tcp: use rds_destroy_pending() to synchronize
       netns/module teardown and rds connection/workq management")
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>