[NET]: uninline dev_alloc_skb, de-bloats a lot

Allyesconfig (v2.6.24-mm1):

-23668  392 funcs, 104 +, 23772 -, diff: -23668 --- dev_alloc_skb

Without many debug CONFIGs (v2.6.25-rc2-mm1):

-12178  382 funcs, 157 +, 12335 -, diff: -12178 --- dev_alloc_skb
dev_alloc_skb                 |  +37

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>