ksmbd: align aux_payload_buf to avoid OOB reads in cryptographic operations

The aux_payload_buf allocation in SMB2 read is performed without ensuring
alignment, which could result in out-of-bounds (OOB) reads during
cryptographic operations such as crypto_xor or ghash. This patch aligns
the allocation of aux_payload_buf to prevent these issues.
(Note that to add this patch to stable would require modifications due
to recent patch "ksmbd: use __GFP_RETRY_MAYFAIL")

Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>