skb allocation / cosumption tracer - Add consumption tracepoint

This patch adds a tracepoint to skb_copy_datagram_iovec, which is called each
time a userspace process copies a frame from a socket receive queue to a user
space buffer.  It allows us to hook in and examine each sk_buff that the system
receives on a per-socket bases, and can be use to compile a list of which skb's
were received by which processes.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>

 include/trace/events/skb.h |   20 ++++++++++++++++++++
 net/core/datagram.c        |    3 +++
 2 files changed, 23 insertions(+)
Signed-off-by: David S. Miller <davem@davemloft.net>