adb: keep all asocket operations in the main thread.

As far as I can see, all asockets operations happen in fdevent_loop()
in the main thread, excepting close_all_sockets(). Instead of adding
lock and ref_count for each asocket, a simpler way would be moving
close_all_sockets() from input_thread to the main thread.

In input_thread(), there are two path to break the loop and call
close_all_sockets(). One path is when receiving offline A_SYNC, which
is sent by the main thread. The other path is when read_packet
fails, which I believe is almost not possible and doesn't matter
(Because t->fd is closed just before t is freed.). So I move
close_all_sockets() to handle_offline() in the main thread.

the socket_list_lock in sockets.cpp could be removed. But I prefer
to leave it for the following changes.

Bug: 6558362
Change-Id: I5da23f60a67a331262c62693b9b127fe2689c799

adb/adb.cpp

@@ -243,6 +243,11 @@ void handle_offline(atransport *t)
     D("adb: offline\n");
     //Close the associated usb
     t->online = 0;
+
+    // This is necessary to avoid a race condition that occured when a transport closes
+    // while a client socket is still active.
+    close_all_sockets(t);
+
     run_transport_disconnects(t);
 }
 

adb/transport.cpp

@@ -330,10 +330,6 @@ static void *input_thread(void *_t)
         put_apacket(p);
     }
 
-    // this is necessary to avoid a race condition that occured when a transport closes
-    // while a client socket is still active.
-    close_all_sockets(t);
-
     D("%s: transport input thread is exiting, fd %d\n", t->serial, t->fd);
     kick_transport(t);
     transport_unref(t);