Increase TTL for offer from 7 to 8 min.

We got reports that offers got removed and re-added even if the maker
had good network connections. Seems the network did not propagate the
refresh msg in time or get too crowded. Increasing the TTl should help
to make those cases more rare. To decrease the refresh rate from 5 min
to 4 min. might be more risky as it would create much more traffic.

core/src/main/java/bisq/core/offer/OfferPayload.java

@@ -356,7 +356,7 @@ public static OfferPayload fromProto(PB.OfferPayload proto) {
 
     @Override
     public long getTTL() {
-        return TimeUnit.MINUTES.toMillis(7);
+        return TimeUnit.MINUTES.toMillis(8);
     }
 
     @Override