net: batch of last_rx update avoidance in ethernet drivers.

None of those drivers uses last_rx for its own needs.

See 4dc89133 ("net: add a comment on
netdev->last_rx") for reference.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Zhangfei Gao <zhangfei.gao@linaro.org>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Wingman Kwok <w-kwok2@ti.com>
Cc: Murali Karicheri <m-karicheri2@ti.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: David S. Miller <davem@davemloft.net>