cifs: Move and expand MAX_SERVER_SIZE definition

MAX_SERVER_SIZE has been moved to cifs_mount.h and renamed
CIFS_NI_MAXHOST for clarity.  It has been expanded to 1024 as the
previous value of 16 was very short.

Signed-off-by: Scott Lovenberg <scott.lovenberg@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>