hs: ADD_ONION with NEW:BEST is still pinned on v2

Even though the control spec says:

  (The "NEW:BEST" option obeys the HiddenServiceVersion torrc option default
  value. Since 0.3.5.1-alpha, it is 3. For Tor versions before 0.3.5.1-alpha,
  default HiddenServiceVersion is 2.)

... in control.c, the ADD_ONION command has this condition that basically pins the NEW:BEST to v2:

    if (!strcasecmp(key_type_rsa1024, key_blob) ||
        !strcasecmp(key_type_best, key_blob)) {
      /* "RSA1024", RSA 1024 bit, also currently "BEST" by default. */

Not good! NEW:BEST should obey the default version, not something hardcoded like so. This will need a spec update to mention the correct tor version.