net: Add missing kernel-doc for netdev ptype lists

.//include/linux/netdevice.h:1826: warning: No description found for parameter 'ptype_all'
.//include/linux/netdevice.h:1826: warning: No description found for parameter 'ptype_specific'

Introduced by commit 7866a621 ("dev: add per net_device packet type
chains")

Cc: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>