remote-curl: store the protocol version the server responded with

remote-curl: store the protocol version the server responded with

Store the protocol version the server responded with when performing
discovery.  This will be used in a future patch to either change the
'Git-Protocol' header sent in subsequent requests or to determine if a
client needs to fallback to using a different protocol version.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>