Add a proto_dhcp_restart() handler that re-acquires the DHCP lease via a
single ubus call, releasing the previous lease and triggering a fresh
DHCPDISCOVER without bouncing the interface.
The re-acquire is implemented by sending SIGHUP to udhcpc, which releases
the current lease (if any) and immediately transitions the state machine
to INIT_SELECTING so the next main-loop iteration sends a fresh
DHCPDISCOVER. A single signal thus expresses 'release this lease and get
a new one' without exiting the client, so upstream watchdogs (e.g. a
DNS-health monitor) can request a clean re-lease without tearing down the
interface.
Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
b8175a021b