s3:smbd: make get_file_handle_for_metadata() public

We won't use it at the end, because a full SMB_VFS_CREATE turns out to
be too expensive. This will be dropped later.

Signed-off-by: Ralph Boehme <rb@sernet.de>
s3: smbd: add flag smb2_crtctx_aapl_readdir_attr

This gets set to true when server and OS X client agree on using this
fearure in an AAPL smb2 create context.

Signed-off-by: Ralph Boehme <rb@sernet.de>
s3: add SMB2 create context AAPL

Signed-off-by: Ralph Boehme <rb@sernet.de>
s3: add AAPL create context flags

Signed-off-by: Ralph Boehme <rb@sernet.de>
s3:smb2_server: AAPL create context

Signed-off-by: Ralph Boehme <rb@sernet.de>