[NET]: skb_trim audit

I found a few more spots where pskb_trim_rcsum could be used but were not.
This patch changes them to use it.

Also, sk_filter can get paged skb data.  Therefore we must use pskb_trim
instead of skb_trim.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>