adb: disable checksum on new versions

The checksum is unnecessary. Improves adb performance by 40% on USB2.

Test: new adb works with new + old adbd, old adb works with new adbd
bug 67327728

Change-Id: I761d8a5a62deaea9bbb092ea9926b2d6d312f00d
diff --git a/adb/adb.cpp b/adb/adb.cpp
index 6b30be8..0e38897 100644
--- a/adb/adb.cpp
+++ b/adb/adb.cpp
@@ -240,7 +240,10 @@
     D("Calling send_connect");
     apacket* cp = get_apacket();
     cp->msg.command = A_CNXN;
-    cp->msg.arg0 = t->get_protocol_version();
+    // Send the max supported version, but because the transport is
+    // initialized to A_VERSION_MIN, this will be compatible with every
+    // device.
+    cp->msg.arg0 = A_VERSION;
     cp->msg.arg1 = t->get_max_payload();
 
     std::string connection_str = get_connection_string();