It seems IP_FREEBIND is a quite useful socket option. It would be nice to have it documented. Sorry no patch, because i don't know enough to write a correct description. I checked with the web (www.kernel.org/doc/man-pages/) version at the time of opening this bug.
I fixed this after a more recent bug report, 20082. *** This bug has been marked as a duplicate of bug 20082 ***