Count packets dropped due to buffer or skb allocation errors.
Report as part of rx_dropped.

v2: drop the ethtool -S entry [Vladimir]
Reviewed-by: NMichael Chan <michael.chan@broadcom.com>
Reviewed-by: NEdwin Peer <edwin.peer@broadcom.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>