The RSA, DH, and ECDH temporary key callbacks expect the number of keybits
for the key (expressed in RSA key bits, which makes *no sense* for ECDH) as
their second argument, not zero.

(jsing@ notes that the RSA callback is only invoked for 'export' ciphers,
which have been removed from LibreSSL, and for the SSL_OP_EPHEMERAL_RSA
option, which is makes the application non-compliant.  More fuel for the
tedu fire...)

jasper@ noted the breakage and bisected it down to the diff that broke this
ok jsing@ miod@