net: log an error rather than asserting if send version is misused

Also cleaned up the comments and moved from the header to the .cpp so that
logging headers aren't needed from net.h

src/net.cpp

@@ -689,6 +689,33 @@ bool CNode::ReceiveMsgBytes(const char *pch, unsigned int nBytes, bool& complete
     return true;
 }
 
+void CNode::SetSendVersion(int nVersionIn)
+{
+    // Send version may only be changed in the version message, and
+    // only one version message is allowed per session. We can therefore
+    // treat this value as const and even atomic as long as it's only used
+    // once a version message has been successfully processed. Any attempt to
+    // set this twice is an error.
+    if (nSendVersion != 0) {
+        error("Send version already set for node: %i. Refusing to change from %i to %i", id, nSendVersion, nVersionIn);
+    } else {
+        nSendVersion = nVersionIn;
+    }
+}
+
+int CNode::GetSendVersion() const
+{
+    // The send version should always be explicitly set to
+    // INIT_PROTO_VERSION rather than using this value until SetSendVersion
+    // has been called.
+    if (nSendVersion == 0) {
+        error("Requesting unset send version for node: %i. Using %i", id, INIT_PROTO_VERSION);
+        return INIT_PROTO_VERSION;
+    }
+    return nSendVersion;
+}
+
+
 int CNetMessage::readHeader(const char *pch, unsigned int nBytes)
 {
     // copy data to temporary parsing buffer

src/net.h

@@ -723,25 +723,8 @@ public:
     {
         return nRecvVersion;
     }
-    void SetSendVersion(int nVersionIn)
-    {
-        // Send version may only be changed in the version message, and
-        // only one version message is allowed per session. We can therefore
-        // treat this value as const and even atomic as long as it's only used
-        // once the handshake is complete. Any attempt to set this twice is an
-        // error.
-        assert(nSendVersion == 0);
-        nSendVersion = nVersionIn;
-    }
-
-    int GetSendVersion() const
-    {
-        // The send version should always be explicitly set to
-        // INIT_PROTO_VERSION rather than using this value until the handshake
-        // is complete.
-        assert(nSendVersion != 0);
-        return nSendVersion;
-    }
+    void SetSendVersion(int nVersionIn);
+    int GetSendVersion() const;
 
     CNode* AddRef()
     {