BUILD: ssl: fix libressl build again after aes-gcm-enc

BUILD: ssl: fix libressl build again after aes-gcm-enc

Enabling aes-gcm-enc in last commit (MINOR: ssl: enable aes_gcm_dec
on LibreSSL) uncovered a wrong condition on the define of the
EVP_CTRL_AEAD_SET_IVLEN macro which I forgot to add when making the
commit, resulting in breaking libressl build again. In case libressl
later defines this macro, the test will have to change for a version
range instead.