esp_aes_gcm_update_ad() function
This function feeds an input buffer as associated data (authenticated but not encrypted data) in a GCM encryption or decryption operation. Call this function after mbedtls_gcm_starts() to pass the associated data. If the associated data is empty, you do not need to call this function. You may not call this function after calling mbedtls_cipher_update().
Arguments
ctx
The GCM context. This must have been started with mbedtls_gcm_starts() and must not have yet received any input with mbedtls_gcm_update().
aad
The buffer holding the additional data, or \c NULL if \p aad_len is \c 0.
aad_len
The length of the additional data. If \c 0, \p add may be \c NULL.
Return value
\c 0 on success.