vfs_syscalls.c::flags_to_right(): O_DSYNC should be allowed for CAP_FSYNC

Noted by:	arrowd
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D53315

share/man/man4/rights.4

@@ -281,7 +281,8 @@ Permit
 and
 .Xr openat 2
 with
-.Dv O_FSYNC
+.Dv O_DSYNC ,
+.Dv O_FSYNC ,
 or
 .Dv O_SYNC
 flag.

sys/kern/vfs_syscalls.c

@@ -1119,7 +1119,7 @@ flags_to_rights(int flags, cap_rights_t *rightsp)
 	if (flags & O_TRUNC)
 		cap_rights_set_one(rightsp, CAP_FTRUNCATE);
 
-	if (flags & (O_SYNC | O_FSYNC))
+	if (flags & (O_SYNC | O_FSYNC | O_DSYNC))
 		cap_rights_set_one(rightsp, CAP_FSYNC);
 
 	if (flags & (O_EXLOCK | O_SHLOCK))