fm10k: fix switch manager high CPU usage

fm10k: fix switch manager high CPU usage

fm10k switch core uses source MAC + VID + SGLORT to do
look up in MAC table. If no match, an exception interrupt
will be sent to the switch manager. Too much of this kind
of exception interrupts cause switch manager side high CPU
usage.
To reproduce this issue, one DPDK testpmd runs on a server
with one fm10k NIC, mac forwards test traffic from one of
fm10k ports to another port. The CPU usage for the switch
manager will go up to about 20% for test traffic rate at
10G bps, comparing to near 0% for no test traffic.

This patch fixes this issue. A default SGLORT is assigned
to each TX queue. This default value works for non-VMDq mode
and current VMDq example. For advanced VMDq usage, e.g.
different source MAC address for different TX queue, FTAG
forwarding function could be used to change this default
SGLORT value.

Fixes: 9ae6068c86da ("fm10k: add dev start/stop")

Signed-off-by: Shaopeng He <shaopeng.he@intel.com>
Acked-by: Jing Chen <jing.d.chen@intel.com>