can: peak/pcie_fd: remove useless code when interface starts

When an interface starts, the echo_skb array is empty and the network
queue should be started only. This patch replaces useless code and locks
when the internal RX_BARRIER message is received from the IP core, telling
the driver that tx may start.

Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>