The RSA, DH, and ECDH temporary key callbacks expect the number of keybits

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@