Although the server_name extension was intended to be extensible to new name
types, OpenSSL 1.0.x had a bug which meant different name types will cause an
error. Further, RFC 4366 originally defined syntax inextensibly. RFC 6066
corrected this mistake, but adding new name types is no longer feasible.
Act as if the extensibility does not exist to simplify parsing. This also
aligns with OpenSSL 1.1.x's behavior. See upstream's
062178678f5374b09f00d70796f6e692e8775aca and
https://www.ietf.org/mail-archive/web/tls/current/msg19425.html
Change-Id: I5af26516e8f777ddc1dab5581ff552daf2ea59b5
Reviewed-on: https://boringssl-review.googlesource.com/7294
Reviewed-by: David Benjamin <davidben@google.com>