[lwip-devel] Build error if LWIP_6LOWPAN && !LWIP_UDP

[Axel Lin]

Got build error if:
#define LWIP_IPV6          1
#define LWIP_6LOWPAN      1
#define LWIP_UDP                0

cc -g -Wall -DLWIP_DEBUG -pedantic -Werror -Wparentheses
-Wsequence-point -Wswitch-default -Wextra -Wundef -Wshadow
-Wpointer-arith -Wcast-qual -Wc++-compat -Wwrite-strings
-Wold-style-definition -Wcast-align -Wmissing-prototypes
-Wredundant-decls -Wnested-externs -Wno-address -Wunreachable-code
-Wuninitialized -Wlogical-op -I. -I../../..
-I../../../../lwip/src/include -I../../../ports/unix/port/include
-I../../../../mbedtls/include -Wno-redundant-decls
-DLWIP_HAVE_MBEDTLS=1 -c ../../../../lwip/src/netif/lowpan6.c
../../../../lwip/src/netif/lowpan6.c: In function ‘lowpan6_frag’:
../../../../lwip/src/netif/lowpan6.c:453:23: error: ‘UDP_HLEN’
undeclared (first use in this function)
       pbuf_header(p, -UDP_HLEN);
                       ^~~~~~~~
../../../../lwip/src/netif/lowpan6.c:453:23: note: each undeclared
identifier is reported only once for each function it appears in
../../../../lwip/src/netif/lowpan6.c: In function ‘lowpan6_decompress’:
../../../../lwip/src/netif/lowpan6.c:702:47: error: ‘UDP_HLEN’
undeclared (first use in this function)
   q = pbuf_alloc(PBUF_IP, p->len + IP6_HLEN + UDP_HLEN, PBUF_POOL);
                                               ^~~~~~~~
../../../../lwip/src/netif/lowpan6.c:924:15: error: dereferencing
pointer to incomplete type ‘struct udp_hdr’
         udphdr->src = lwip_htons(lowpan6_buffer[lowpan6_offset] << 8
| lowpan6_buffer[lowpan6_offset + 1]);
               ^~
../../Common.allports.mk:94: recipe for target 'lowpan6.o' failed
make: *** [lowpan6.o] Error 1