tests: add socket tagging test for qtaguid kernel netfilter module

tests: add socket tagging test for qtaguid kernel netfilter module

Add a small test to verify that socket tagging is not hopelessly
broken.

Test for
 - invalid: arg count, command, tags.
 - double tagging
 - acct_tag changing
 - optional uid
 - 64bit unsigned vs signed
 - invalid sock_fd
 - multiple entries
 - untagging
 - uid/gid checking + max tags.

It tries its best to allow concurrent invocations, but it just
can not be sure that it always detects the in-kernel addresses of
the sockets it has tagged.

Change-Id: I4e372fcddbd0b1cd6ba5d8be4692e0f31ec71a99