scripted-diff: test: Use int.to_bytes over struct packing

-BEGIN VERIFY SCRIPT-
 sed -i --regexp-extended 's!struct.pack\(.<?B., (.*)\)!\1.to_bytes(1, "little")!g'             $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.<I., (.*)\)!\1.to_bytes(4, "little")!g'              $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.<H., (.*)\)!\1.to_bytes(2, "little")!g'              $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.<i., (.*)\)!\1.to_bytes(4, "little", signed=True)!g' $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.<q., (.*)\)!\1.to_bytes(8, "little", signed=True)!g' $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.>H., (.*)\)!\1.to_bytes(2, "big")!g'                 $( git grep -l struct.pack )
-END VERIFY SCRIPT-

test/functional/test_framework/p2p.py

@@ -411,7 +411,7 @@ class P2PConnection(asyncio.Protocol):
             tmsg = self.magic_bytes
             tmsg += msgtype
             tmsg += b"\x00" * (12 - len(msgtype))
-            tmsg += struct.pack("<I", len(data))
+            tmsg += len(data).to_bytes(4, "little")
             th = sha256(data)
             h = sha256(th)
             tmsg += h[:4]