addmultisigaddress creates an address respecting the setting, being unable to generate a specific type of address without also adding it to the wallet seems wrong.

I suppose in the future `addresstype` may be refactored to be wallet-specific, which would leave this non-wallet rpc call without an argument. Perhaps there should just be an optional parameter to set it.
static UniValue createmultisig(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() < 2 || request.params.size() > 3)
    {
        std::string msg = "createmultisig nrequired [\"key\",...] ( \"address_type\" )\n"
            "\nCreates a multi-signature address with n signature of m keys required.\n"
            "It returns a json object with the address and redeemScript.\n"
            "\nArguments:\n"
            "1. nrequired                    (numeric, required) The number of required signatures out of the n keys.\n"
            "2. \"keys\"                       (string, required) A json array of hex-encoded public keys\n"
            "     [\n"
            "       \"key\"                    (string) The hex-encoded public key\n"
            "       ,...\n"
            "     ]\n"
            "3. \"address_type\"               (string, optional) The address type to use. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\". Default is legacy.\n"
            "\nResult:\n"
            "{\n"
            "  \"address\":\"multisigaddress\",  (string) The value of the new multisig address.\n"
            "  \"redeemScript\":\"script\"       (string) The string value of the hex-encoded redemption script.\n"
            "}\n"
            "\nExamples:\n"
            "\nCreate a multisig address from 2 public keys\n"
            + HelpExampleCli("createmultisig", "2 \"[\\\"03789ed0bb717d88f7d321a368d905e7430207ebbd82bd342cf11ae157a7ace5fd\\\",\\\"03dbc6764b8884a92e871274b87583e6d5c2a58819473e17e107ef3f6aa5a61626\\\"]\"") +
            "\nAs a json rpc call\n"
            + HelpExampleRpc("createmultisig", "2, \"[\\\"03789ed0bb717d88f7d321a368d905e7430207ebbd82bd342cf11ae157a7ace5fd\\\",\\\"03dbc6764b8884a92e871274b87583e6d5c2a58819473e17e107ef3f6aa5a61626\\\"]\"")
        ;
        throw std::runtime_error(msg);