Allow multipathing between PSMX and DDSI

Once upon a time sending a sample to a single destination via PSMX and DDSI at the same
time would lead to stuttering because of insufficient precise filtering in the delivery
paths, but that problem has been fixed a long time ago (I think in commit
ef91c27).  For a long time, no-one realised that the bit
that prevented this from happening was left in.

Signed-off-by: Erik Boasson <eb@ilities.com>

src/core/ddsi/src/ddsi_wraddrset.c

@@ -324,9 +324,7 @@ static const int32_t cost_discarded = 1;
 
 // Cost associated with delivering another time to a reader that has
 // already been covered by a (selected) PSMX locator.
-// Currently, it is quite painful when this happens because it can
-// lead to user observable stuttering.
-static const int32_t cost_redundant_psmx = 1000000;
+static const int32_t cost_redundant_psmx = 0;
 
 // Cost associated with delivering data for the first time (slightly
 // negative cost makes it possible to give a slightly higher initial