package/netperf: move SITE so s.b.o

The original site is gone.

Fixes:
http://autobuild.buildroot.net/results/8d4a2ef5a7f50ea21b844d6cf806bb83016ae17b/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/netperf/netperf.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 NETPERF_VERSION = 2.7.0
-NETPERF_SITE = ftp://ftp.netperf.org/netperf
+NETPERF_SITE = http://sources.buildroot.org/netperf
 NETPERF_SOURCE = netperf-$(NETPERF_VERSION).tar.bz2
 # gcc 5+ defaults to gnu99 which breaks netperf
 NETPERF_CONF_ENV = \