e1000e: partial revert of 790b3d96 plus FC workraround for 82577/8

e1000e: partial revert of 790b3d96 plus FC workraround for 82577/8

Commit 790b3d96bfb6e91cde71876a23ada98b1d62e7bd broke Tx/Rx when using
jumbo frames on certain parts (i.e. only PAUSE frames could be exchanged
once the high water mark was reached preventing normal packet traffic).
This patch reverts the breakage and sets appropriate high and low water
marks of the Rx FIFO for 82577/82578 which require a workaround due to a
flow control issue in hardware.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>