send-pack: send push options correctly in stateless-rpc case

send-pack: send push options correctly in stateless-rpc case

"git send-pack --stateless-rpc" puts each request in a sequence of pkt-lines
followed by a flush-pkt. The push option code forgot about this and sends push
options and their terminating delimiter as ordinary pkt-lines that get their
length header stripped off by remote-curl before being sent to the server.

The result is multiple malformed requests, which the server rejects.

Fortunately send-pack --stateless-rpc already is aware of this "pkt-line within
pkt-line" framing for the update commands that precede push options. Handle
push options the same way.

Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>