O2net: Disallow o2net accept connection request from itself.

Currently, o2net_accept_one() is allowed to accept a connection from
listening node itself, such a fake connection will not be successfully
established due to no handshake detected afterwards, and later end up
with triggering connecting worker in a loop.

We're going to fix this by treating such connection request as 'invalid',
since we've got no chance of requesting connection from a node to itself
in a OCFS2 cluster.

The fix doesn't hurt user's scan for o2net-listener, it always gets a
successful connection from userpace.

Signed-off-by: Tristan Ye <tristan.ye@oracle.com>
Acked-by: Sunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>