Improve backwards compat with 1.0.2 for ECDHParameters

Improve backwards compat with 1.0.2 for ECDHParameters

In 1.0.2 you could configure automatic ecdh params by using the
ECDHParameters config directive and setting it to the value
"+Automatic" or just "Automatic". This is no longer required in 1.1.0+
but we still recognise the "+Automatic" keyword for backwards compatibility.
However we did not recognise just "Automatic" without the leading "+" which
is equally valid. This commit fixes that omission.

Fixes #4113

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6035)