Bug 1084342: Copy received ancillary data into |SocketMessageWatcher|, r=shawnjohnjr

The cast-and-assign pattern for retrieving file descriptors is prone to
SIGBUS signals on platforms that don't support unaligned memory access.
This patch fixes the problem by copying the received data directly.

dom/bluetooth/bluedroid/BluetoothSocketMessageWatcher.cpp

@@ -232,7 +232,7 @@ SocketMessageWatcher::RecvMsg2()
         TEMP_FAILURE_RETRY(close(mClientFd));
       }
       // retrieve sent client fd
-      mClientFd = *(static_cast<int*>(CMSG_DATA(cmsgptr)));
+      memcpy(&mClientFd, CMSG_DATA(cmsgptr), sizeof(mClientFd));
     }
   }
 

dom/bluetooth2/bluedroid/BluetoothSocketMessageWatcher.cpp

@@ -232,7 +232,7 @@ SocketMessageWatcher::RecvMsg2()
         TEMP_FAILURE_RETRY(close(mClientFd));
       }
       // retrieve sent client fd
-      mClientFd = *(static_cast<int*>(CMSG_DATA(cmsgptr)));
+      memcpy(&mClientFd, CMSG_DATA(cmsgptr), sizeof(mClientFd));
     }
   }