learning-switch: Make lswitch own its rconn.

learning-switch: Make lswitch own its rconn.

Until now, ovs-controller and the learning-switch code split responsibility
for the OpenFlow connection.  This commit moves all the responsibility into
the learning-switch code.

The rationale here is twofold.  First, the split itself seems odd; I think
there must have been a reason for it at one time, but I don't remember it
and don't see one anymore.  Second, I intend to make the lswitch code more
stateful in upcoming commits, and it seems odd to have the lswitch manage
quite a bit of state but not the entity that that state applies to.

Signed-off-by: Ben Pfaff <blp@nicira.com>