transport-helper: call do_take_over() in connect_helper

transport-helper: call do_take_over() in connect_helper

After successfully connecting to the smart transport by calling
process_connect_service() in connect_helper(), run do_take_over() to
replace the old vtable with a new one which has methods ready for the
smart transport connection. This fixes the exit code of git-archive
in test case "archive remote http repository" of t5003.

The connect_helper() function is used as the connect method of the
vtable in "transport-helper.c", and it is called by transport_connect()
in "transport.c" to setup a connection. The only place that we call
transport_connect() so far is in "builtin/archive.c". Without running
do_take_over(), it may fail to call transport_disconnect() in
run_remote_archiver() of "builtin/archive.c". This is because for a
stateless connection and a service like "git-upload-archive", the
remote helper may receive a SIGPIPE signal and exit early. Call
do_take_over() to have a graceful disconnect method, so that we still
call transport_disconnect() even if the remote helper exits early.

Helped-by: Linus Arver <linusa@google.com>
Signed-off-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>