esp32/network_lan: Fix LAN.isconnected().

nic.isconnected() returns now "True", if a) the physical link is up and b)
an IP address is assigned.  The latter happens often by DHCP, in which case
an active connection can be assumed.  If the IP address is set manually,
nic.isconnected() would report "True" as well, if at least the physical
link is up.  This matches WLAN behaviour which returns "True" when the WLAN
has an IP address.

Before, the behaviour of nic.isconneceted() was erratic, returning "True"
sometimes even without a Ethernet cable attached.

Fixes issue #12741.

Signed-off-by: robert-hh <robert@hammelrath.com>

ports/esp32/network_lan.c

@@ -325,7 +325,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(lan_status_obj, lan_status);
 
 STATIC mp_obj_t lan_isconnected(mp_obj_t self_in) {
     lan_if_obj_t *self = MP_OBJ_TO_PTR(self_in);
-    return self->base.active ? mp_obj_new_bool(self->phy->get_link(self->phy) == ETH_LINK_UP) : mp_const_false;
+    return mp_obj_new_bool(self->base.active && (eth_status == ETH_GOT_IP));
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(lan_isconnected_obj, lan_isconnected);