[NET]: uninline skb_trim, de-bloats

Allyesconfig (v2.6.24-mm1):
-10976  209 funcs, 123 +, 11099 -, diff: -10976 --- skb_trim

Without number of debug related CONFIGs (v2.6.25-rc2-mm1):
-7360  192 funcs, 131 +, 7491 -, diff: -7360 --- skb_trim
skb_trim                      |  +42

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