ocfs2: Start the ocfs2_control handshake.

When a control daemon opens the ocfs2_control device, it must perform a
handshake to tell the filesystem it is something capable of monitoring
cluster status.  Only after the handshake is complete will the filesystem
allow mounts.

This is the first part of the handshake.  The daemon reads all supported
ocfs2_control protocols, then writes in the protocol it will use.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>