e17: connman: ipv4_method can be NULL
e17: connman: ipv4_method can be NULL

Fix segv: properties can be NULL, so it's not a good thing to use with
strcmp.



git-svn-id: 6ac5796aeae0cef97fb47bcc287d4ce899c6fa6e@57948 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33

jordemort/e17,jordemort/e17,jordemort/e17