Bump PROTOCOL_VERSION to 70216 (#3287)

We removed "alert" p2p message and changed "mempool" message behaviour a bit. It probably makes sense to bump PROTOCOL_VERSION now. This should also help to distinguish v0.15 nodes from late v0.14.0.x ones.

Author: UdjinM6

src/version.h

@@ -11,7 +11,7 @@
  */
 
 
-static const int PROTOCOL_VERSION = 70215;
+static const int PROTOCOL_VERSION = 70216;
 
 //! initial proto version, to be increased after version/verack negotiation
 static const int INIT_PROTO_VERSION = 209;