nvmeofgw: propagate quorum feature to the NVMeofMonClient,

nvmeofgw: propagate quorum feature to the NVMeofMonClient,
          reverted feature bit NVMEOF_BEACON_DIFF:

   -NVMeofGwMon adds a quorum_features indication to the MonClient map.
   -MonClient initially sends beacons without applying the BEACON_DIFF logic.
   -MonClient begins applying the BEACON_DIFF logic only when the BEACON_DIFF bit
    is set in the quorum_features field of the NVMeoF monitor map.
   -added mon commands:
     nvme-gw set beacon-diff disable
     nvme-gw set beacon-diff enable
   -performed changes in encode/decode of the BEACON_DIFF feature
   -reverted NVMEOF_BEACON_DIFF bit

Signed-off-by: Leonid Chernin <leonidc@il.ibm.com>