e1000e: 82579 unaccounted missed packets

On 82579, there is a hardware bug that can cause received packets to not
get transferred from the PHY to the MAC due to K1 (a power saving feature
of the PHY-MAC interconnect similar to ASPM L1).  Since the MAC controls
the accounting of missed packets, these will go unnoticed.  Workaround the
issue by setting the K1 beacon duration according to the 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>
Signed-off-by: David S. Miller <davem@davemloft.net>