learning-switch: Don't limit message queued by --with-flows.

queue_tx() intentionally limits the number of outstanding OpenFlow messages
queued to the switch.  This was unintentionally being applied to the
messages queued to the switch at startup by ovs-ofctl's --with-flows
command.  This patch should fix the problem, by calling rconn_send()
directly instead of through queue_tx().

Ahmed reported that with this patch there was still a problem when 30,000
flows were specified in the file.

Reported-by: Ahmed Bilal <numan252@gmail.com>