net: lib: dhcpv4: goto INIT on IF down, not RENEWING

When the interface goes down, the safest thing to do is to return to
the INIT state, as there is no guarantee that any state is preserved
upon the interface coming back up again.

This is particularly the case with WiFi.

Signed-off-by: Jordan Yates <[email protected]>
(cherry picked from commit 0f56974)

Author: JordanYates

subsys/net/lib/dhcpv4/dhcpv4.c

@@ -1160,7 +1160,7 @@ static void dhcpv4_iface_event_handler(struct net_mgmt_event_callback *cb,
 
 		if (iface->config.dhcpv4.state == NET_DHCPV4_BOUND) {
 			iface->config.dhcpv4.attempts = 0U;
-			iface->config.dhcpv4.state = NET_DHCPV4_RENEWING;
+			iface->config.dhcpv4.state = NET_DHCPV4_INIT;
 			NET_DBG("enter state=%s", net_dhcpv4_state_name(
 					iface->config.dhcpv4.state));
 			/* Remove any bound address as interface is gone */