RDMA/nes: Lock down connected_nodes list while processing it

While processing connected_nodes list, we would release the lock when
we need to send reset to remote partner.  That created a window where
the list can be modified.  Change this into a two step process: place
nodes that need processing on a local list then process the local list.

Signed-off-by: Faisal Latif <faisal.latif@intel.com>
Signed-off-by: Chien Tung <chien.tin.tung@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>