net: bcmgenet: Be drop monitor friendly

There are 3 spots where we call dev_kfree_skb() but we are actually
just doing a normal SKB consumption: __bcmgenet_tx_reclaim() for normal
TX reclamation, bcmgenet_alloc_rx_buffers() during the initial RX ring
setup and bcmgenet_free_rx_buffers() during RX ring cleanup.

Fixes: d6707bec ("net: bcmgenet: rewrite bcmgenet_rx_refill()")
Fixes: f48bed16 ("net: bcmgenet: Free skb after last Tx frag")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>