linux_dep: Generalise tcp_info.h to handling Linux extension compatibility

tcp_info.h exists just to contain a modern enough version of struct
tcp_info for our needs, removing compile time dependency on the version of
kernel headers.  There are several other cases where we can remove similar
compile time dependencies on kernel version.  Prepare for that by renaming
tcp_info.h to linux_dep.h.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

linux_dep.h

@@ -1,13 +1,15 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later
  * Copyright Red Hat
  *
- * Largely derived from include/linux/tcp.h in the Linux kernel
+ * Declarations for Linux specific dependencies
  */
 
-#ifndef TCP_INFO_H
-#define TCP_INFO_H
+#ifndef LINUX_DEP_H
+#define LINUX_DEP_H
 
 /* struct tcp_info_linux - Information from Linux TCP_INFO getsockopt()
+ *
+ * Largely derived from include/linux/tcp.h in the Linux kernel
  *
  * Some fields returned by TCP_INFO have been there for ages and are shared with
  * BSD.  struct tcp_info from netinet/tcp.h has only those fields.  There are
@@ -117,4 +119,4 @@ struct tcp_info_linux {
 						 */
 };
 
-#endif /* TCP_INFO_H */
+#endif /* LINUX_DEP_H */

tcp.c

@@ -299,10 +299,10 @@
 #include "log.h"
 #include "inany.h"
 #include "flow.h"
+#include "linux_dep.h"
 
 #include "flow_table.h"
 #include "tcp_internal.h"
-#include "tcp_info.h"
 #include "tcp_buf.h"
 
 /* MSS rounding: see SET_MSS() */