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.



SVN revision: 57948

tasn/enlightenment,tizenorg/platform.upstream.enlightenment,FlorentRevest/Enlightenment,rvandegrift/e,FlorentRevest/Enlightenment,tizenorg/platform.upstream.enlightenment,tizenorg/platform.upstream.enlightenment,tasn/enlightenment,FlorentRevest/Enlightenment,tasn/enlightenment,rvandegrift/e,rvandegrift/e