DHCP request send on reboot does not contain hostname option

When the network is changed, dhcp is rebooted.
It will send a dhcp request again to verify it's lease.

DHCP requests are send out in selecting state, rebinding, renewing
and rebooting. But in the rebooting state the hostname option is
not included. This means that after reboot, the hostname will be
unknown to the DNS.

Signed-off-by: Simon Goldschmidt <goldsimon@gmx.de>

src/core/ipv4/dhcp.c

@@ -1286,6 +1286,11 @@ dhcp_reboot(struct netif *netif)
     for (i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++) {
       options_out_len = dhcp_option_byte(options_out_len, msg_out->options, dhcp_discover_request_options[i]);
     }
+
+#if LWIP_NETIF_HOSTNAME
+    options_out_len = dhcp_option_hostname(options_out_len, msg_out->options, netif);
+#endif /* LWIP_NETIF_HOSTNAME */
+
     LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, DHCP_STATE_REBOOTING, msg_out, DHCP_REQUEST, &options_out_len);
     dhcp_option_trailer(options_out_len, msg_out->options, p_out);