rpc/util: multisig: only check redeemScript size is <= 520 for P2SH

This increase the maximum number of pubkeys to 20 (valid in P2WSH and
P2SH-P2WSH) and only checks the redeemScript doesn't exceed
MAX_SCRIPT_ELEMENT_SIZE for P2SH, as this checked is removed under
Segwit context.

Signed-off-by: Antoine Poinsot <darosior@protonmail.com>

src/rpc/util.cpp

@@ -231,16 +231,12 @@ CTxDestination AddAndGetMultisigDestination(const int required, const std::vecto
     if ((int)pubkeys.size() < required) {
         throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("not enough keys supplied (got %u keys, but need at least %d to redeem)", pubkeys.size(), required));
     }
-    if (pubkeys.size() > 16) {
-        throw JSONRPCError(RPC_INVALID_PARAMETER, "Number of keys involved in the multisignature address creation > 16\nReduce the number");
+    if (pubkeys.size() > MAX_PUBKEYS_PER_MULTISIG) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Number of keys involved in the multisignature address creation > %d\nReduce the number", MAX_PUBKEYS_PER_MULTISIG));
     }
 
     script_out = GetScriptForMultisig(required, pubkeys);
 
-    if (script_out.size() > MAX_SCRIPT_ELEMENT_SIZE) {
-        throw JSONRPCError(RPC_INVALID_PARAMETER, (strprintf("redeemScript exceeds size limit: %d > %d", script_out.size(), MAX_SCRIPT_ELEMENT_SIZE)));
-    }
-
     // Check if any keys are uncompressed. If so, the type is legacy
     for (const CPubKey& pk : pubkeys) {
         if (!pk.IsCompressed()) {
@@ -249,6 +245,10 @@ CTxDestination AddAndGetMultisigDestination(const int required, const std::vecto
         }
     }
 
+    if (type == OutputType::LEGACY && script_out.size() > MAX_SCRIPT_ELEMENT_SIZE) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, (strprintf("redeemScript exceeds size limit: %d > %d", script_out.size(), MAX_SCRIPT_ELEMENT_SIZE)));
+    }
+
     // Make the address
     CTxDestination dest = AddAndGetDestinationForScript(keystore, script_out, type);