dcrutil: Lookup params by addr prefix in chaincfg.

This modifies the code that looks up the params by a given network
prefix to make use of the new function provided by chaincfg in order to
ensure that it works with all registered networks as the package was
intended.

dcrutil/address.go

@@ -205,19 +205,7 @@ func detectNetworkForAddress(addr string) (*chaincfg.Params, error) {
 		return nil, fmt.Errorf("empty string given for network detection")
 	}
 
-	networkChar := addr[0:1]
-	switch networkChar {
-	case chaincfg.MainNetParams.NetworkAddressPrefix:
-		return &chaincfg.MainNetParams, nil
-	case chaincfg.TestNet3Params.NetworkAddressPrefix:
-		return &chaincfg.TestNet3Params, nil
-	case chaincfg.SimNetParams.NetworkAddressPrefix:
-		return &chaincfg.SimNetParams, nil
-	case chaincfg.RegNetParams.NetworkAddressPrefix:
-		return &chaincfg.RegNetParams, nil
-	}
-
-	return nil, fmt.Errorf("unknown network type in string encoded address")
+	return chaincfg.ParamsByNetAddrPrefix(addr[0:1])
 }
 
 // AddressPubKeyHash is an Address for a pay-to-pubkey-hash (P2PKH)