smb: smbdirect: introduce smbdirect_get_buf_page_count()

smb: smbdirect: introduce smbdirect_get_buf_page_count()

This is a copy of get_buf_page_count() in the server
and will replace it soon.

The only difference is that we now use size_t instead
of int.

Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>