dhcpcd: install dhcpcd as /usr/sbin/dhcpcd.

GNU/Linux distributions usually install dhcpcd in /usr/sbin.
NetworkManager will look for it in this directory.

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Acked-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>