net/mosquitto: bump to 1.6.4

Full changelog here: https://mosquitto.org/blog/2019/08/version-1-6-4-released/

Fixes a regression in persistent session handling, and various other
regressions related to the mqtt5 support.

Signed-off-by: Karl Palsson <karlp@etactica.com>

net/mosquitto/Makefile

@@ -9,7 +9,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=mosquitto
-PKG_VERSION:=1.6.3
+PKG_VERSION:=1.6.4
 PKG_RELEASE:=1
 PKG_LICENSE:=BSD-3-Clause
 PKG_LICENSE_FILES:=LICENSE.txt
@@ -17,7 +17,7 @@ PKG_CPE_ID:=cpe:/a:eclipse:mosquitto
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://mosquitto.org/files/source/
-PKG_HASH:=9ef5cc75f4fe31d7bf50654ddf4728ad9e1ae2e5609a4b42ecbbcb4a209ed17e
+PKG_HASH:=a3d5822c249f6a6e13311b1b09eff6807ea01608a5a77934e1769842e9d146ef
 PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(BUILD_VARIANT)/$(PKG_NAME)-$(PKG_VERSION)
 
 include $(INCLUDE_DIR)/package.mk