Fix send_command in BluetoothUserSocket (#4754)

Author: gpotter2

scapy/layers/bluetooth.py

@@ -3128,7 +3128,7 @@ def __init__(self, adapter_index=0):
             sock_address=sa)
 
     def send_command(self, cmd):
-        opcode = cmd.opcode
+        opcode = cmd[HCI_Command_Hdr].opcode
         self.send(cmd)
         while True:
             r = self.recv()