SSL: select the right key type for kx
SSL: select the right key type for kx

During the switch to BoringSSL this function was rewritten and it
requested DH public key with RSA signature for a lot of things.

Bug: 20641394
Change-Id: Id3880b01ed1810c5d7af9996c48ce45fdf4850f8

google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt