adb: Add "adb disconnect" command for disconnecting TCP/IP devices.

Also check that device is not already connected in "adb connect"

Change-Id: I5f84b56b63d8c6932f23791cac319fd6bc39d36c
Signed-off-by: Mike Lockwood <lockwood@android.com>
diff --git a/adb/transport_local.c b/adb/transport_local.c
index c528d1f..81d120e 100644
--- a/adb/transport_local.c
+++ b/adb/transport_local.c
@@ -204,6 +204,7 @@
 {
     int fd = t->sfd;
     t->sfd = -1;
+    adb_shutdown(fd);
     adb_close(fd);
 
 #if ADB_HOST