netperf: bump to version 2.7.0

Also add hash file.
And work around gcc 5+ defaulting to gnu99, fixes:

http://autobuild.buildroot.net/results/077/077714a0ee67057abcff680b244228a409243bbf/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/netperf/netperf.hash

@@ -0,0 +1,2 @@
+# Locally calculated
+sha256	842af17655835c8be7203808c3393e6cb327a8067f3ed1f1053eb78b4e40375a	netperf-2.7.0.tar.bz2

package/netperf/netperf.mk

@@ -4,9 +4,13 @@
 #
 ################################################################################
 
-NETPERF_VERSION = 2.6.0
+NETPERF_VERSION = 2.7.0
 NETPERF_SITE = ftp://ftp.netperf.org/netperf
-NETPERF_CONF_ENV = ac_cv_func_setpgrp_void=set
+NETPERF_SOURCE = netperf-$(NETPERF_VERSION).tar.bz2
+# gcc 5+ defaults to gnu99 which breaks netperf
+NETPERF_CONF_ENV = \
+	ac_cv_func_setpgrp_void=set \
+	CFLAGS="$(TARGET_CFLAGS) -std=gnu89"
 NETPERF_CONF_OPTS = --enable-demo=yes
 NETPERF_LICENSE = netperf license
 NETPERF_LICENSE_FILES = COPYING