dhcpcd: security bump to version 6.4.3

Issue and CVE req: http://seclists.org/oss-sec/2014/q3/261


Patch upstreamed in a subtly different way.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>