dropbear: add default config file to disable root login

root login is disabled by default for openssh and we can
enable it through IMAGE_FEATURES 'debug-tweaks' or
'allow-empty-password', so change to the same default
behavior for dropbear.

(From OE-Core rev: d3e69fa2fef83015658aa5fa1442bab5a8c3edaa)

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/dropbear/dropbear.inc

@@ -19,6 +19,7 @@ SRC_URI = "http://matt.ucc.asn.au/dropbear/releases/dropbear-${PV}.tar.bz2 \
            file://dropbearkey.service \
            file://dropbear@.service \
            file://dropbear.socket \
+           file://dropbear.default \
            ${@bb.utils.contains('DISTRO_FEATURES', 'pam', '${PAM_SRC_URI}', '', d)} "
 
 PAM_SRC_URI = "file://0005-dropbear-enable-pam.patch \
@@ -62,6 +63,8 @@ do_install() {
 		${D}${sbindir} \
 		${D}${localstatedir}
 
+	install -m 0644 ${WORKDIR}/dropbear.default ${D}${sysconfdir}/default/dropbear
+
 	install -m 0755 dropbearmulti ${D}${sbindir}/
 	ln -s ${sbindir}/dropbearmulti ${D}${bindir}/dbclient
 

meta/recipes-core/dropbear/dropbear/dropbear.default

@@ -0,0 +1,2 @@
+# Disallow root logins by default
+DROPBEAR_EXTRA_ARGS="-w"