BUG/MINOR: ssl: abort on sni allocation failure

BUG/MINOR: ssl: abort on sni allocation failure

The ssl_sock_add_cert_sni() function never return an error when a
sni_ctx allocation fail. It silently ignores the problem and continues
to try to allocate other snis.

It is unlikely that a sni allocation will succeed after one failure and
start a configuration without all the snis. But to avoid any problem we
return a -1 upon an sni allocation error and stop the configuration
parsing.

This patch must be backported in every version supporting the crt-list
sni filters. (as far as 1.5)