Send RESYNCING while performing resync start/stop

When a resync is initiated, RESYNCING message is sent to all active
nodes with the range (lo,hi). When the resync is over, a RESYNCING
message is sent with (0,0). A high sector value of zero indicates
that the resync is over.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>