lx: re-graft AmneziaWG 2.0 obfuscation onto sagernet/wireguard-go v0.0.5

Rebase of the AWG obf graft (was e5feca7 on v0.0.3) onto v0.0.5
(2c27bbf4f9, 'Add L3 forwarding support'). 15 of 16 graft files
applied clean via 3-way; only send.go conflicted, on a single line
(upstream queuedOutboundPackets backpressure decrement vs a graft
blank line — took upstream).

Key invariant preserved: MessageEncapsulatingTransportSize=0 (graft
zeroes the sagernet encapsulating headroom; AWG obfuscation composes
the prefix itself via SendBuffers, not Bind.Send prepend). Upstream's
InputPacket/InputPackets and the new size-based outbound buffer pool
(GetOutboundBuffer/PutOutboundBuffer) are taken verbatim; the graft's
RoutineEncryption (header at buffer start) and transport-padding shift
in RoutineSequentialSender re-woven around them.

Builds clean on linux/android/windows/darwin (device/conn/tun).

device/cookie.go

@@ -118,6 +118,7 @@ func (st *CookieChecker) CreateReply(
 	msg []byte,
 	recv uint32,
 	src []byte,
+	msgType uint32,
 ) (*MessageCookieReply, error) {
 	st.RLock()
 
@@ -153,7 +154,7 @@ func (st *CookieChecker) CreateReply(
 	smac1 := smac2 - blake2s.Size128
 
 	reply := new(MessageCookieReply)
-	reply.Type = MessageCookieReplyType
+	reply.Type = msgType
 	reply.Receiver = recv
 
 	_, err := rand.Read(reply.Nonce[:])