Commit 9151c7015e introduced support for the global DHCP DUID to
generate a RFC4361-style client identifier.
However, the IAID introduced in those changes is based on ifindex, which
is subject to changes and causes issues on environments requiring a stable
IAID.
This commit switches the IAID to a stable one based on MD5.
Fixes: 9151c7015e ("netifd: use the global DHCP DUID for DHCPv4")
Link: https://github.com/openwrt/openwrt/pull/21489
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
e1c125c167