add missing header end comments

- ensures a consistent usage in header files
- also add a blank line after the copyright header where missing
- also remove orphan new-lines at the end of some files

src/netbase.h

@@ -182,4 +182,4 @@ bool CloseSocket(SOCKET& hSocket);
 /** Disable or enable blocking-mode for a socket */
 bool SetSocketNonBlocking(SOCKET& hSocket, bool fNonBlocking);
 
-#endif
+#endif // BITCOIN_NETBASE_H