e1000e: workaround link issues on busy hub in half duplex on 82577/82578

This patch removes a delay in hardware after every received packet allowing
more time for transmitted packets to go out in between received packets in
half duplex.

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>