Fix error code on __zpl_ioctl_setflags()

Other (all?) Linux filesystems seem to return -EPERM instead of -EACCESS
when trying to set FS_APPEND_FL or FS_IMMUTABLE_FL without the
CAP_LINUX_IMMUTABLE capability.  This was detected by generic/545 test
in the fstest suite.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Luis Henriques <henrix@camandro.org>
Closes #11791

module/os/linux/zfs/zpl_file.c

@@ -867,7 +867,7 @@ __zpl_ioctl_setflags(struct inode *ip, uint32_t ioctl_flags, xvattr_t *xva)
 	if ((fchange(ioctl_flags, zfs_flags, FS_IMMUTABLE_FL, ZFS_IMMUTABLE) ||
 	    fchange(ioctl_flags, zfs_flags, FS_APPEND_FL, ZFS_APPENDONLY)) &&
 	    !capable(CAP_LINUX_IMMUTABLE))
-		return (-EACCES);
+		return (-EPERM);
 
 	if (!zpl_inode_owner_or_capable(kcred->user_ns, ip))
 		return (-EACCES);