Read initial ack for scp

OpenSSH's scp sends an initial ack after the arguments (see scp.c:sink
in line 914 of CVS version 1.171). We did not read this initial ack,
and hence the protocol on gerrit side got out of sync with the
client. This problem introduced a race condition, which could manifest
in a "lost connection" message on the scp client side.

We now read the client's initial ack, and thereby get gerrit and scp
in sync again.

Change-Id: Ic6f42aee69e1163bff1f22b40f16a00fc366f902
1 file changed