ixgbe: Limit SFP polling rate

ixgbe: Limit SFP polling rate

Orabug: 21918732

Reduce the frequency of polling for SFP modules. Because the
service task sometimes runs at high rates, we can poll for
SFPs too often. When an SFP is not present, the I2C timeouts
that result are very costly. So, prevent SFP polling from
being done more than once every two seconds. To reduce latency,
the poll time is cleared in a couple of cases to permit the
next service task execution to poll the SFP module.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit 58e7cd24d474c87763387f606e403012f562760b)
Signed-off-by: Brian Maly <brian.maly@oracle.com>