Fix "address.GetPort() != 0" assertion for helpers on FreeBSD (at least).

Fix "address.GetPort() != 0" assertion for helpers on FreeBSD (at least).

The order (or set of?) #include files used by src/ssl/helper.cc (and
probably by other helper source files) has changed recently, exposing a
defines.h dependency on sys/socket.h where that system header is
required to define AF_UNIX. With AF_UNIX incorrectly undefined,
IPC_STREAM was set to IPC_TCP_SOCKET instead of IPC_UNIX_STREAM, and
helpers that do not have a notion of a listening port, were trying to
create communication sockets using TCP streams, triggering a "must have
a port" assertion in comm_connect_addr() called from ipcCreate().

TODO: Moving IPC_* defines into an IPC-specific header file may be a
better solution then exposing all defines.h users to sys/socket.h.