add new linux file sealing api to fcntl.h

new in linux v3.17 commit 40e041a2c858b3caefc757e26cb85bfceae5062b
sealing allows some operations to be blocked on a file which makes
file access safer when fds are shared between processes (only
supported for shared mem fds currently)

flags:
F_SEAL_SEAL prevents further sealing
F_SEAL_SHRINK prevents file from shrinking
F_SEAL_GROW prevents file from growing
F_SEAL_WRITE prevents writes

fcntl commands:
F_GET_SEALS get the current seal flags
F_ADD_SEALS add new seal flags

include/fcntl.h

@@ -121,6 +121,13 @@ int posix_fallocate(int, off_t, off_t);
 #define F_CANCELLK	1029
 #define F_SETPIPE_SZ	1031
 #define F_GETPIPE_SZ	1032
+#define F_ADD_SEALS	1033
+#define F_GET_SEALS	1034
+
+#define F_SEAL_SEAL	0x0001
+#define F_SEAL_SHRINK	0x0002
+#define F_SEAL_GROW	0x0004
+#define F_SEAL_WRITE	0x0008
 
 #define DN_ACCESS	0x00000001
 #define DN_MODIFY	0x00000002