Update EVP_CIPHER_CTX_set_padding documentation.

value is an internal value which may not have a corresponding OBJECT

IDENTIFIER.

EVP_CIPHER_CTX_set_padding() enables or disables padding. By default

encryption operations are padded using standard block padding and the

padding is checked and removed when decrypting. If the B<pad> parameter

is zero then no padding is performed, the total amount of data encrypted

or decrypted must then be a multiple of the block size or an error will

occur.

EVP_CIPHER_CTX_set_padding() enables or disables padding. This

function should be called after the context is set up for encryption

or decryption with EVP_EncryptInit_ex(), EVP_DecryptInit_ex() or

EVP_CipherInit_ex(). By default encryption operations are padded using

standard block padding and the padding is checked and removed when

decrypting. If the B<pad> parameter is zero then no padding is

performed, the total amount of data encrypted or decrypted must then

be a multiple of the block size or an error will occur.

EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key

length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>