Support IPPROTO_IP level and IP_PKTINFO option in setsockopt

[robgjansen]

Let's add a new test case to support those options to make sure we get the behavior correct when implementing it in Shadow.

See also the mailing list thread starting here:
http://mailman.cs.umn.edu/archives/shadow-support/2016-August/000552.html

[robgjansen]

I'm looking for the following in order to make progress on this issue:

a. explain the expected behavior from the kernel on the issue linked above
b. write a very small test case that tests for that behavior, and submit a pull request for the test case that I can merge into shadow

For b., see the example test cases in shadow/src/test - just copy a small one like the sleep test and modify to exercise and check the expected behavior. This way I will know when I have Shadow producing the correct result.