package/dbus: set session-socket-dir to /tmp

dbus has a session socket directory configuration setting,
that, if not set, will be autodeducted based on env vars
like TMPDIR during configuration time.

Becuse of that, the builder's environment variables will
lead to an image with a broken session bus while
leaking builder's details to the image.

Add an explicit setting of session-socket-dir to /tmp dir.

Fixes: https://gitlab.com/buildroot.org/buildroot/-/issues/67

Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
Reviewed-by: Fiona Klute <fiona.klute@gmx.de>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>
(cherry picked from commit f777c7991275c62f2881d1dae0c2aa357a7f1a21)
Signed-off-by: Thomas Perale <thomas.perale@mind.be>

package/dbus/dbus.mk

@@ -34,6 +34,7 @@ DBUS_CONF_OPTS = \
 	--disable-doxygen-docs \
 	--with-system-socket=/run/dbus/system_bus_socket \
 	--with-system-pid-file=/run/messagebus.pid \
+	--with-session-socket-dir=/tmp \
 	--runstatedir=/run
 
 ifeq ($(BR2_STATIC_LIBS),y)