Adding method GetTotalSize() to CTransaction

GetTotalSize() returns the total transaction size (including witness) in
bytes.

src/primitives/transaction.cpp

@@ -131,6 +131,11 @@ unsigned int CTransaction::CalculateModifiedSize(unsigned int nTxSize) const
     return nTxSize;
 }
 
+unsigned int CTransaction::GetTotalSize() const
+{
+    return ::GetSerializeSize(*this, SER_NETWORK, PROTOCOL_VERSION);
+}
+
 std::string CTransaction::ToString() const
 {
     std::string str;

src/primitives/transaction.h

@@ -415,6 +415,13 @@ public:
 
     // Compute modified tx size for priority calculation (optionally given tx size)
     unsigned int CalculateModifiedSize(unsigned int nTxSize=0) const;
+    
+    /**
+     * Get the total transaction size in bytes, including witness data.
+     * "Total Size" defined in BIP141 and BIP144.
+     * @return Total transaction size in bytes
+     */
+    unsigned int GetTotalSize() const;
 
     bool IsCoinBase() const
     {