tests: net: sockets: add tests for SO_REUSEADDR

This commit adds unit tests for the SO_REUSEADDR socket option to test
the different possible scenarios for the option to work correctly.

There is also a fix for the TCP testsuite to make a now failing test
pass again due to a TIME_WAIT socket.

Signed-off-by: Tobias Frauenschläger <t.frauenschlaeger@me.com>