net.c: move fallback definition of struct mmsghdr to a separate file.

* msghdr.h: New file.
* Makefile.am (strace_SOURCES): Add it.
* net.c: Include it.  Move fallback definition of struct mmsghdr there.
* tests/mmsg.c: Include "msghdr.h".  Remove fallback definition
of struct mmsghdr.

Makefile.am

@@ -153,6 +153,7 @@ strace_SOURCES =	\
 	mount.c		\
 	mpers_type.h	\
 	mq.c		\
+	msghdr.h	\
 	mtd.c		\
 	native_defs.h	\
 	net.c		\

msghdr.h

@@ -0,0 +1,14 @@
+#ifndef MSGHDR_H_
+# define MSGHDR_H_
+
+/* For definitions of struct msghdr and struct mmsghdr. */
+# include <sys/socket.h>
+
+# ifndef HAVE_STRUCT_MMSGHDR
+struct mmsghdr {
+	struct msghdr msg_hdr;
+	unsigned msg_len;
+};
+# endif
+
+#endif /* MSGHDR_H_ */

net.c

@@ -29,6 +29,7 @@
  */
 
 #include "defs.h"
+#include "msghdr.h"
 #include <sys/stat.h>
 #include <sys/socket.h>
 #include <sys/uio.h>
@@ -440,13 +441,6 @@ struct mmsghdr32 {
 	uint32_t /* unsigned */ msg_len;
 };
 
-#ifndef HAVE_STRUCT_MMSGHDR
-struct mmsghdr {
-	struct msghdr msg_hdr;
-	unsigned msg_len;
-};
-#endif
-
 #if SUPPORTED_PERSONALITIES > 1 && SIZEOF_LONG > 4
 static void
 copy_from_msghdr32(struct msghdr *to_msg, struct msghdr32 *from_msg32)

tests/mmsg.c

@@ -36,14 +36,8 @@
 # include <errno.h>
 # include <stdio.h>
 # include <unistd.h>
-# include <sys/socket.h>
 
-# ifndef HAVE_STRUCT_MMSGHDR
-struct mmsghdr {
-	struct msghdr msg_hdr;
-	unsigned msg_len;
-};
-# endif
+# include "msghdr.h"
 
 static int
 send_mmsg(int fd, struct mmsghdr *vec, unsigned int vlen, unsigned int flags)