include: posix: add c++ extern scope

`<fcntl.h>`, `<net/if.h>`, and `<netinet/tcp.h>` were missing
`extern "C" { .. }"` which is required to avoid C++ name
mangling.

Signed-off-by: Chris Friedt <[email protected]>

Author: cfriedt

include/zephyr/posix/fcntl.h

@@ -27,7 +27,15 @@
 #define F_GETFL 3
 #define F_SETFL 4
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 int open(const char *name, int flags, ...);
 int fcntl(int fildes, int cmd, ...);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* ZEPHYR_POSIX_FCNTL_H_ */

include/zephyr/posix/net/if.h

@@ -8,4 +8,12 @@
 
 #include <zephyr/net/socket.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* ZEPHYR_INCLUDE_POSIX_NET_IF_H_ */

include/zephyr/posix/netinet/tcp.h

@@ -8,4 +8,12 @@
 
 #include <zephyr/net/socket.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* ZEPHYR_INCLUDE_POSIX_NETINET_TCP_H_ */