protobuf: bump to 2.6.1

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/protobuf/protobuf.hash

@@ -0,0 +1,2 @@
+# Locally calculated
+sha256 2667b7cda4a6bc8a09e5463adf3b5984e08d94e72338277affa8594d8b6e5cd1 protobuf-v2.6.1.tar.gz

package/protobuf/protobuf.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-PROTOBUF_VERSION = v2.5.0
+PROTOBUF_VERSION = v2.6.1
 PROTOBUF_SITE = $(call github,google,protobuf,$(PROTOBUF_VERSION))
 PROTOBUF_LICENSE = BSD-3c
 PROTOBUF_LICENSE_FILES = COPYING.txt