Added config file for avahi-daemon

Without this config file, avahi-daemon would not startup because of "Failed to create server: No suitable network protocol available" error, which is fixed by following configuration setting in /etc/avahi/avahi-daemon.conf:
disallow-other-stacks=yes

recipes-connectivity/avahi/avahi_0.6.31.bbappend

@@ -0,0 +1,10 @@
+# prepend this dir to path, to find conf file
+FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+
+SRC_URI += "file://avahi-daemon.conf"
+
+do_install_append () {
+      install -m 0644 ${WORKDIR}/avahi-daemon.conf ${D}${sysconfdir}/avahi/avahi-daemon.conf
+}
+
+INC := "${@int(PRINC) + 2}"