Crypto/chcr: fix gcm-aes and rfc4106-gcm failed tests

This patch fixes two issues observed during self tests with
CONFIG_CRYPTO_MANAGER_EXTRA_TESTS enabled.

1. gcm(aes) hang issue , that happens during decryption.
2. rfc4106-gcm-aes-chcr encryption unexpectedly succeeded.

For gcm-aes decryption , authtag is not mapped due to
sg_nents_for_len(upto size: assoclen+ cryptlen - authsize).
So fix it by dma_mapping authtag.
Also replaced sg_nents() to sg_nents_for_len() in case of aead_dma_unmap().

For rfc4106-gcm-aes-chcr, used crypto_ipsec_check_assoclen() for checking
the validity of assoclen.

Signed-off-by: Ayush Sawal <ayush.sawal@chelsio.com>
Signed-off-by: Devulapally Shiva Krishna <shiva@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>