ar71xx: add missing return statement in ethernet mtu change op

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37756 3c298f89-4303-0410-b956-a3cf2f4a3e73
ar71xx: ethernet: do not update the unused dev->last_rx field

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37757 3c298f89-4303-0410-b956-a3cf2f4a3e73
ar71xx: ethernet: skip calls to netdev_completed_queue and netif_wake_queue if no tx cleanup was done

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37758 3c298f89-4303-0410-b956-a3cf2f4a3e73