memcached: upgrade to 1.4.31

This should also fix the build errors, which are reported by
LEDE buildbots, e.g. at:
https://downloads.lede-project.org/snapshots/faillogs/arm_cortex-a7_neon-vfpv4/packages/memcached/compile.txt

While at, also fix the licensing information.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

net/memcached/Makefile

@@ -9,15 +9,19 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=memcached
-PKG_VERSION:=1.4.26
+PKG_VERSION:=1.4.31
 PKG_RELEASE:=1
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=http://memcached.org/files
-PKG_MD5SUM:=59b7bbfbc9cde5731bf4446e1e37b440
-PKG_INSTALL:=1
+PKG_MD5SUM:=c19bb0e77e720f64f33ecb43de28a1b4
+
 PKG_MAINTAINER:=Thomas Heil <heil@terminal-consulting.de>
-PKG_LICENSE:=permissive free software license
+
+PKG_LICENSE:=BSD-3-Clause
+PKG_LICENSE_FILES:=COPYING
+
+PKG_INSTALL:=1
 
 include $(INCLUDE_DIR)/package.mk