usb: gadget: NCM: differentiate consumed packets from dropped packets

dev_kfree_skb_any() is used to free packets that are dropped by the
network stack. Therefore the function should not be used for packets
that have been successfully processed by the network stack. Instead
dev_consume_skb_any() has to be used for such consumed packets.

This separation helps to identify dropped packets.

Signed-off-by: Torsten Polle <tpolle@de.adit-jv.com>
Signed-off-by: Harish Jenny K N <harish_kandiga@mentor.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>