build: Fix client and server only builds

Also correct LwIP build directory.

examples/lwip/Makefile

@@ -7,7 +7,7 @@
 # This file is part of the CoAP C library libcoap. Please see README and
 # COPYING for terms of use.
 
-libcoap_dir = ../../
+libcoap_dir = ../..
 
 LIBCOAP_API_VERSION = $(shell if [ -f $(libcoap_dir)/configure.ac ];  then \
           sed -ne 's/^LIBCOAP_API_VERSION=\([0-9]\+\).*$$/\1/p' $(libcoap_dir)/configure.ac; \

src/coap_io.c

@@ -398,7 +398,9 @@ void coap_socket_close(coap_socket_t *sock) {
                   coap_socket_strerror(), errno);
       }
     }
+#if COAP_SERVER_SUPPORT
     sock->endpoint = NULL;
+#endif /* COAP_SERVER_SUPPORT */
     sock->session = NULL;
 #endif /* COAP_EPOLL_SUPPORT */
     coap_closesocket(sock->fd);

src/net.c

@@ -1088,7 +1088,9 @@ coap_client_delay_first(coap_session_t *session)
     session->delay_recursive = 0;
     coap_session_release(session);
   }
-#endif /* COAP_CLIENT_SUPPORT */
+#else /* ! COAP_CLIENT_SUPPORT */
+  (void)session;
+#endif /* ! COAP_CLIENT_SUPPORT */
   return 1;
 }