Merge ed9dabe088 into 1cc1536e6a

This took some figuring out, it might be obvious to those familiar with
lwipcfg.h but for someone picking this up for the first time to experiment on
linux, this helpful comment would have helped enormously.

contrib/ports/unix/setup-tapif

@@ -12,6 +12,9 @@
 # Enter 192.168.1.200 or "http://lwip.local/" (Zeroconf)
 # in your webbrowser to see example_app webpage.
 
+# N.b. you must disable USE_DHCP and USE_AUTOIP in lwipcfg.h for the static 
+# ip 192.168.1.200 to work in tapif
+
 export PRECONFIGURED_TAPIF=tap0
 
 sudo ip tuntap add dev $PRECONFIGURED_TAPIF mode tap user `whoami`

src/api/sockets.c

@@ -2926,6 +2926,7 @@ lwip_sockopt_to_ipopt(int optname)
 static void
 lwip_getsockopt_impl_ipv6_checksum(int s, struct lwip_sock* sock, void* optval)
 {
+  LWIP_UNUSED_ARG(s);
   if (sock->conn->pcb.raw->chksum_reqd == 0) {
     *(int*)optval = -1;
   }
@@ -2939,6 +2940,7 @@ lwip_getsockopt_impl_ipv6_checksum(int s, struct lwip_sock* sock, void* optval)
 static int
 lwip_setsockopt_impl_ipv6_checksum(int s, struct lwip_sock* sock, const void* optval, socklen_t optlen)
 {
+  LWIP_UNUSED_ARG(s);
   /* It should not be possible to disable the checksum generation with ICMPv6
    * as per RFC 3542 chapter 3.1 */
   if (sock->conn->pcb.raw->protocol == IPPROTO_ICMPV6) {