This commit modifies the behavior of `parse_extended_address` in such a way
that if it fails, it will always return a `BAD_HOSTNAME` value, which is then
used to return the 0xF6 extended error code. This way, in any case that is
not a valid v2 address, we return the 0xF6 error code, which is the expected
behavior.
Signed-off-by: David Goulet <dgoulet@torproject.org>
