package/iputils: move binaries to the location also used by Busybox

package/iputils: move binaries to the location also used by Busybox

iputils installs several programs that are also implemented as applets
in Busybox. Two of these (arping and tftpd) are installed by iputils
in /bin, while Busybox installs them in /usr/sbin, causing both to be
present if both iputils and busybox are enabled.

This commit moves the binaries installed by iputils to /usr/sbin, so
that only these are installed (Busybox will be installed later thanks
to its optional dependency on iputils, but it will not override the
tools installed by iputils).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>