r3279: Removed MSG_DONTWAIT flags as many platform don't have it.

r3279: Removed MSG_DONTWAIT flags as many platform don't have it.

If a socket is non-blocking then adding MSG_DONTWAIT is pointless (it
does nothing), so all we lose is the ability to set non-blocking on a
packet-by-packet basis, which is not a very useful thing to have
anyway

if the socket is blocking then the code already adds MSG_WAITALL, so
MSG_DONTWAIT is also not needed in that case.
(This used to be commit b8a2afae67691a609b4a7a577fee3f9518adc9d2)