LU-9480 lnet: introduce LNET_PEER_MULTI_RAIL flag bit

LU-9480 lnet: introduce LNET_PEER_MULTI_RAIL flag bit

Add lp_state as a flag word to lnet_peer, and add lp_lock
to protect it. This lock needs to be taken whenever the
field is updated, because setting or clearing a bit is
a read-modify-write cycle.

The lp_multi_rail is removed, its function is replaced by
the new LNET_PEER_MULTI_RAIL flag bit.

The helper lnet_peer_is_multi_rail() tests the bit.

Test-Parameters: trivial
Signed-off-by: Olaf Weber <olaf@sgi.com>
Change-Id: I15034be7670bcb18460dc709accf675711a48113
Reviewed-on: https://review.whamcloud.com/25781
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: Amir Shehata <amir.shehata@intel.com>
Tested-by: Amir Shehata <amir.shehata@intel.com>