iperf3: update URL

Update iperf3 to point to the correct project website. Prior URL was the
old iperf2 website.

Signed-off-by: Karl Palsson <karlp@remake.is>

SVN-Revision: 47184

package/network/utils/iperf3/Makefile

@@ -27,7 +27,7 @@ define Package/iperf3
   SECTION:=net
   CATEGORY:=Network
   TITLE:=Internet Protocol bandwidth measuring tool
-  URL:=http://sourceforge.net/projects/iperf/
+  URL:=https://github.com/esnet/iperf
 endef
 
 TARGET_CFLAGS += -D_GNU_SOURCE