cifs: new nt status codes from MS-SMB2

MS-SMB2 spec has introduced two new status codes,
STATUS_SERVER_UNAVAILABLE and STATUS_FILE_NOT_AVAILABLE
which are to be treated as retryable errors.

This change adds these to the available mappings and
maps them to Linux errno EAGAIN.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

smb: move client and server files to common directory fs/smb

Move CIFS/SMB3 related client and server files (cifs.ko and ksmbd.ko
and helper modules) to new fs/smb subdirectory:

fs/cifs --> fs/smb/client
fs/ksmbd --> fs/smb/server
fs/smbfs_common --> fs/smb/common

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>