smb: client: insert compression check/call on write requests

On smb2_async_writev(), set CIFS_COMPRESS_REQ on request flags if
should_compress() returns true.

On smb_send_rqst() check the flags, and compress and send the request to
the server.

(*) If the compression fails with -EMSGSIZE (i.e. compressed size is >=
uncompressed size), the original uncompressed request is sent instead.

Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>