Fix _socket compilation failures on non-Linux buildbots (cf. issue #1746656).

Modules/socketmodule.h

@@ -59,9 +59,12 @@ typedef int socklen_t;
 #include <bluetooth.h>
 #endif
 
+#ifdef HAVE_NET_IF_H
+# include <net/if.h>
+#endif
+
 #ifdef HAVE_NETPACKET_PACKET_H
 # include <sys/ioctl.h>
-# include <net/if.h>
 # include <netpacket/packet.h>
 #endif
 

configure

@@ -6037,7 +6037,7 @@ sys/lock.h sys/mkdev.h sys/modem.h \
 sys/param.h sys/poll.h sys/select.h sys/sendfile.h sys/socket.h sys/statvfs.h \
 sys/stat.h sys/termio.h sys/time.h \
 sys/times.h sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h pty.h \
-libutil.h sys/resource.h netpacket/packet.h sysexits.h bluetooth.h \
+libutil.h sys/resource.h net/if.h netpacket/packet.h sysexits.h bluetooth.h \
 bluetooth/bluetooth.h linux/tipc.h spawn.h util.h
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`

configure.in

@@ -1293,7 +1293,7 @@ sys/lock.h sys/mkdev.h sys/modem.h \
 sys/param.h sys/poll.h sys/select.h sys/sendfile.h sys/socket.h sys/statvfs.h \
 sys/stat.h sys/termio.h sys/time.h \
 sys/times.h sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h pty.h \
-libutil.h sys/resource.h netpacket/packet.h sysexits.h bluetooth.h \
+libutil.h sys/resource.h net/if.h netpacket/packet.h sysexits.h bluetooth.h \
 bluetooth/bluetooth.h linux/tipc.h spawn.h util.h)
 AC_HEADER_DIRENT
 AC_HEADER_MAJOR

pyconfig.h.in

@@ -539,6 +539,9 @@
 /* Define to 1 if you have the <netpacket/packet.h> header file. */
 #undef HAVE_NETPACKET_PACKET_H
 
+/* Define to 1 if you have the <net/if.h> header file. */
+#undef HAVE_NET_IF_H
+
 /* Define to 1 if you have the `nice' function. */
 #undef HAVE_NICE