tls: disable libssl ecdh_auto
tls: disable libssl ecdh_auto

SSL_CTX_set_ecdh_auto is broken as it walks (unconfigured) curve
priority list which means by default that larger curves have more priority.

End result is that "auto" picks sect571t1 (B-571) as preferred curve:

  https://www.ietf.org/mail-archive/web/tls/current/msg17097.html

IOW, "auto" expects that somebody has manually synced curve priority
list with current server key.  This misses the whole point about "auto":
no manual configuration.

This patch uses always compat SSL_CTX_set_ecdh_auto() that simply picks
same curve as used by EC key.  If this is not possible (ECDHE-RSA),
it picks P-256.

mgjv/libusual,rabbitt/libusual,rabbitt/libusual,rabbitt/libusual,markokr/libusual,markokr/libusual,ifduyue/libusual,rabbitt/libusual,ifduyue/libusual,mgjv/libusual,markokr/libusual,mgjv/libusual,ifduyue/libusual,ifduyue/libusual,markokr/libusual,mgjv/libusual