Issue #10141: fix socketmodule compilation on Linux systems with <linux/can.h>
but without AF_CAN definition.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index aac1b72..e64c960 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -1220,7 +1220,7 @@
     }
 #endif
 
-#ifdef HAVE_LINUX_CAN_H
+#ifdef AF_CAN
     case AF_CAN:
     {
         struct sockaddr_can *a = (struct sockaddr_can *)addr;
@@ -1606,7 +1606,7 @@
     }
 #endif
 
-#ifdef HAVE_LINUX_CAN_H
+#ifdef AF_CAN
     case AF_CAN:
         switch (s->sock_proto) {
         case CAN_RAW:
@@ -1746,7 +1746,7 @@
     }
 #endif
 
-#ifdef HAVE_LINUX_CAN_H
+#ifdef AF_CAN
     case AF_CAN:
     {
         *len_ret = sizeof (struct sockaddr_can);