[MINOR] stream_sock: add SI_FL_NOLINGER for faster close

[MINOR] stream_sock: add SI_FL_NOLINGER for faster close

This new flag may be set by any user on a stream interface to tell
the underlying protocol that there is no need for lingering on the
socket since we know the other side either received everything or
does not care about what we sent.

This will typically be used with forced server close in HTTP mode,
where we want to quickly close a server connection after receiving
its response. Otherwise the system would prevent us from reusing
the same port for some time.