add "adb sideload" and sideload connection state

Recovery will soon support a minimal implementation of adbd which will
do nothing but accept downloads from the "adb sideload" command and
install them.  This is the client side command (mostly resurrected out
of the old circa-2007 "adb recover" command) and the new connection
state.

Change-Id: I4f67b63f1b3b38d28c285d1278d46782679762a2
diff --git a/adb/transport.c b/adb/transport.c
index 83a349a..2f7bd27 100644
--- a/adb/transport.c
+++ b/adb/transport.c
@@ -831,6 +831,7 @@
     case CS_DEVICE: return "device";
     case CS_HOST: return "host";
     case CS_RECOVERY: return "recovery";
+    case CS_SIDELOAD: return "sideload";
     case CS_NOPERM: return "no permissions";
     default: return "unknown";
     }