[qa] Build v4 blocks in p2p-compactblocktests

This fixes an issue in backporting to 0.13 as 0.13 enforces SF
activation by block version lockin instead of through a hard-coded
block height.

qa/rpc-tests/p2p-compactblocks.py

@@ -128,6 +128,7 @@ def build_block_on_tip(self, node, segwit=False):
         tip = node.getbestblockhash()
         mtp = node.getblockheader(tip)['mediantime']
         block = create_block(int(tip, 16), create_coinbase(height + 1), mtp + 1)
+        block.nVersion = 4
         if segwit:
             add_witness_commitment(block)
         block.solve()