Merge branch 'bpf-socket-cookie-uid'

Chenbo Feng says:

====================
net: core: Two Helper function about socket information

Introduce two eBpf helper function to get the socket cookie and
socket uid for each packet. The helper function is useful when
the *sk field inside sk_buff is not empty. These helper functions
can be used on socket and uid based traffic monitoring programs.

Change since V7:
* change the user namespace of uid helper function to sock_net(sk)->user_ns

Change since V6:
* change the user namespace of uid helper function back to init_user_ns
  since in some situation, for example, pinned bpf object, the current
  user namespace is not always applicable.

Change since V5:
* Delete unnecessary blank lines in sample program.
* Refine the variable orders in get_uid helper function.

Change since V4:
* Using current user namespace to get uid instead of using init_ns.
* Add compiling setup of example program in to Makefile.
* Change the name style of the example program binaries.

Change since V3:
* Fixed some typos and incorrect comments in sample program
* replaced raw insns with BPF_STX_XADD and add it to libbpf.h
* Use a temp dir as mount point instead and added a check for
  the user input string.
* Make the get uid helper function returns the user namespace uid
  instead of kuid.
* Return a overflowuid instead of 0 when no uid information is found.

Change since V2:
* Add a sample program to demostrate the usage of the helper function.
* Moved the helper function proto invoking place.
* Add function header into tools/include
* Apply sk_to_full_sk() before getting uid.

Change since V1:
* Removed the unnecessary declarations and export command
* resolved conflict with master branch.
* Examine if the socket is a full socket before getting the uid.
====================

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