feat(wallet): Set mnemonic bits default to 128 bits / 12 words

to be more compatible with most wallets out there

Author: UdjinM6

src/hdchain.h

@@ -43,7 +43,7 @@ class CHDChain
 
 public:
     /** Default for -mnemonicbits */
-    static constexpr int DEFAULT_MNEMONIC_BITS = 256; // 256 bits == 24 words
+    static constexpr int DEFAULT_MNEMONIC_BITS = 128; // 128 bits == 12 words
 
     CHDChain() = default;
     CHDChain(const CHDChain& other) :