Clarify SMB2/SMB3 create context and add missing ones

Clarify comments for create contexts which we do send,
and fix typo in one create context definition and add
newer SMB3 create contexts to the list.

Signed-off-by: Steve French <smfrench@gmail.com>

diff --cc fs/cifs/smb2ops.c
Simple merge

diff --cc fs/cifs/smb2pdu.c
Simple merge

diff --cc fs/cifs/smb2pdu.h
Simple merge