net: always dump full packets with skb_dump

Currently skb_dump has a restriction to only dump full packet for the
first 5 socket buffers, then only headers will be printed. Remove this
arbitrary and confusing restriction, which is only documented vaguely
("up to") in the comments above the prototype.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>