BUG/MEDIUM: ECC cert should work with TLS < v1.2 and openssl >= 1.1.1

BUG/MEDIUM: ECC cert should work with TLS < v1.2 and openssl >= 1.1.1

With openssl >= 1.1.1 and boringssl multi-cert is natively supported.
ECDSA/RSA selection is done and work correctly with TLS >= v1.2.
TLS < v1.2 have no TLSEXT_TYPE_signature_algorithms extension: ECC
certificate can't be selected, and handshake fail if no RSA cert
is present. Safe ECC certificate selection without client announcement
can be very tricky (browser compatibilty). The safer approach is to
select ECDSA certificate if no other certificate matches, like it is
with openssl < 1.1.1: certificate selection is only done via the SNI.

Thanks to Lukas Tribus for reporting this and analysing the problem.

This patch should be backported to 1.8