Fix some basic socket issues with tor-fw-helper-natpmp on windows

This isn't going to be the last of these issues, but we might as
well take the fixes as we find them.

Patch from Gisle Vanem, fixes bug 7280.

changes/bug7280

@@ -0,0 +1,4 @@
+  o Minor bugfixes:
+    - Fix some bugs in tor-fw-helper-natpmp when trying to build and
+      run it on Windows. More bugs likely remain. Patch from Gisle Vanem.
+      Fixes bug 7280; bugfix on 0.2.3.1-alpha.

src/tools/tor-fw-helper/tor-fw-helper-natpmp.c

@@ -93,16 +93,20 @@ wait_until_fd_readable(tor_socket_t fd, struct timeval *timeout)
 {
   int r;
   fd_set fds;
+
+#ifndef WIN32
   if (fd >= FD_SETSIZE) {
     fprintf(stderr, "E: NAT-PMP FD_SETSIZE error %d\n", fd);
     return -1;
   }
+#endif
+
   FD_ZERO(&fds);
   FD_SET(fd, &fds);
   r = select(fd+1, &fds, NULL, NULL, timeout);
   if (r == -1) {
     fprintf(stderr, "V: select failed in wait_until_fd_readable: %s\n",
-            strerror(errno));
+            tor_socket_strerror(tor_socket_errno(fd)));
     return -1;
   }
   /* XXXX we should really check to see whether fd was readable, or we timed
@@ -140,12 +144,12 @@ tor_natpmp_add_tcp_mapping(uint16_t internal_port, uint16_t external_port,
     if (is_verbose)
       fprintf(stderr, "V: attempting to readnatpmpreponseorretry...\n");
     r = readnatpmpresponseorretry(&(state->natpmp), &(state->response));
-    sav_errno = errno;
+    sav_errno = tor_socket_errno(state->natpmp.s);
 
     if (r<0 && r!=NATPMP_TRYAGAIN) {
       fprintf(stderr, "E: readnatpmpresponseorretry failed %d\n", r);
       fprintf(stderr, "E: errno=%d '%s'\n", sav_errno,
-              strerror(sav_errno));
+              tor_socket_strerror(sav_errno));
     }
 
   } while (r == NATPMP_TRYAGAIN);
@@ -198,7 +202,7 @@ tor_natpmp_fetch_public_ip(tor_fw_options_t *tor_fw_options,
     if (tor_fw_options->verbose)
       fprintf(stderr, "V: NAT-PMP attempting to read reponse...\n");
     r = readnatpmpresponseorretry(&(state->natpmp), &(state->response));
-    sav_errno = errno;
+    sav_errno = tor_socket_errno(state->natpmp.s);
 
     if (tor_fw_options->verbose)
       fprintf(stderr, "V: NAT-PMP readnatpmpresponseorretry returned"
@@ -208,7 +212,7 @@ tor_natpmp_fetch_public_ip(tor_fw_options_t *tor_fw_options,
       fprintf(stderr, "E: NAT-PMP readnatpmpresponseorretry failed %d\n",
               r);
       fprintf(stderr, "E: NAT-PMP errno=%d '%s'\n", sav_errno,
-              strerror(sav_errno));
+              tor_socket_strerror(sav_errno));
     }
 
   } while (r == NATPMP_TRYAGAIN );