use "IPv6" and "IPv4" in strings as these are the official spellings and make ParseNetwork() in netbase.cpp case-insensitive

src/netbase.cpp

@@ -11,6 +11,7 @@
 #endif
 
 #include "strlcpy.h"
+#include <boost/algorithm/string/case_conv.hpp> // for to_lower()
 
 using namespace std;
 
@@ -27,6 +28,7 @@ static bool vfNoProxy[NET_MAX] = {};
 static const unsigned char pchIPv4[12] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff };
 
 enum Network ParseNetwork(std::string net) {
+    boost::to_lower(net);
     if (net == "ipv4") return NET_IPV4;
     if (net == "ipv6") return NET_IPV6;
     if (net == "tor")  return NET_TOR;