Use the same encryption growth macro consistently

We had two different macros for calculating the potential growth due to
encryption. The macro we use for allocating the underlying buffer should be
the same one that we use for reserving bytes for encryption growth.

Also if we are adding the MAC independently of the cipher algorithm then
the encryption growth will not include that MAC so we should remove it
from the amount of bytes that we reserve for that growth. Otherwise we
might exceed our buffer size and the WPACKET_reserve operation will
fail.

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19264)