In order to prepare for the addition of protocol_v2 push the protocol
version discovery outside of 'get_remote_heads()'. This will allow for
keeping the logic for processing the reference advertisement for
protocol_v1 and protocol_v0 separate from the logic for protocol_v2.
Signed-off-by: Brandon Williams <bmwill@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>