package/dhcpcd: add udev optional dependency

udev is an optional dependency (enabled by default) since version 6.1.0:
https://github.com/rsmarples/dhcpcd/commit/12bbc8cb5c7507be15a7e0af4140c3d81125c46c



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>