BUILD: ssl: fix typo in HAVE_SSL_CTX_ADD_SERVER_CUSTOM_EXT macro

HAVE_SSL_CTX_ADD_SERVER_CUSTOM_EXT was introduced in ec609098718b9c1cd803ca57442b2b98c9ba4a16
however it was defined as HAVE_SL_CTX_ADD_SERVER_CUSTOM_EXT (missing "S")
let us fix typo
2 files changed