rconn: Only increment seqno when connection actually drops or reconnects.

rconn: Only increment seqno when connection actually drops or reconnects.

rconn_get_connection_seqno() is documented to change only when an rconn
connects or disconnnects, but in fact it was also changing whenever an
rconn went into or out of the "idle" state (following sending an echo
request).  This fixes the problem.

rconn_get_connection_seqno() didn't have any existing users, but an
upcoming commit adds one.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Russell Bryant <rbryant@redhat.com>
Acked-by: Justin Pettit <jpettit@nicira.com>