Merge branch 'pskb_extract'

Sowmini Varadhan says:

====================
pskb_extract() helper function.

This patchset follows up on the discussion in
 https://www.mail-archive.com/netdev@vger.kernel.org/msg105090.html

For RDS-TCP, we have to deal with the full gamut of
nonlinear sk_buffs, including all the frag_list variants.
Also, the parent skb has to remain unchanged, while the clone
is queued for Rx on the PF_RDS socket.

Patch 1 of this patchset adds a pskb_extract() function that
does all this without the redundant memcpy's in pskb_expand_head()
and __pskb_pull_tail().

v2: Marcelo Leitner review comments
====================

Signed-off-by: David S. Miller <davem@davemloft.net>