e1000e: 82579 packet drop workaround

In K1 mode (a MAC/PHY interconnect power mode), the 82579 device shuts down
the Phase Lock Loop (PLL) of the interconnect to save power.  When the PLL
starts working, the 82579 device may start to transfer the packet through
the interconnect before it is fully functional causing packet drops.  This
workaround disables shutting down the PLL in K1 mode for 1G link speed.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>