stream: Eliminate pstream_set_dscp().

stream: Eliminate pstream_set_dscp().

This function is really of marginal utility.  This commit drops it and
makes the existing callers instead open a new pstream with the desired
dscp.

The ulterior motive here is that the set_dscp() function that actually sets
the DSCP on a socket really wants to know the address family (AF_INET vs.
AF_INET6).  We could plumb that down through the stream code, and that's
one reasonable option, but I thought that simply eliminating some calls
to set_dscp() where we don't already have the address family handy was
another reasonable way to go.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Alex Wang <alexw@nicira.com>