MFC r253282:

A complete duplication of binding should be allowed if on both new and
duplicated sockets a multicast address is bound and either
SO_REUSEPORT or SO_REUSEADDR is set.

But actually it works for the following combinations:

  * SO_REUSEPORT is set for the fist socket and SO_REUSEPORT for the new;
  * SO_REUSEADDR is set for the fist socket and SO_REUSEADDR for the new;
  * SO_REUSEPORT is set for the fist socket and SO_REUSEADDR for the new;

and fails for this:

  * SO_REUSEADDR is set for the fist socket and SO_REUSEPORT for the new.

Fix the last case.

PR:		179901