loader: move dhcp server in own ifdef

Author: facchinm

Diff for: loader/llext_exports.c

@@ -76,12 +76,15 @@ FORCE_EXPORT_SYM(_net_l2_ETHERNET);
 
 #if defined(CONFIG_NET_DHCPV4)
 FORCE_EXPORT_SYM(net_dhcpv4_start);
-FORCE_EXPORT_SYM(net_dhcpv4_server_start);
 #if defined(CONFIG_NET_DHCPV4_OPTION_CALLBACKS)
 FORCE_EXPORT_SYM(net_dhcpv4_add_option_callback);
 #endif
 #endif
 
+#if defined(CONFIG_NET_DHCPV4_SERVER)
+FORCE_EXPORT_SYM(net_dhcpv4_server_start);
+#endif
+
 #if defined(CONFIG_NET_MGMT_EVENT)
 FORCE_EXPORT_SYM(net_mgmt_add_event_callback);
 FORCE_EXPORT_SYM(net_mgmt_event_wait_on_iface);