rpcserver: use SetBit helper for setting Bolt11 blinded bit

This commit uses the new SetBit helper for setting the Bolt11 route
blinding required bit in a generated invoice. This helper will take care
of setting the dependent bits of the feature bit (namely the route
blinding and TLV feature bits and will use the required variant of
both).

rpcserver.go

@@ -6055,8 +6055,9 @@ func (r *rpcServer) AddInvoice(ctx context.Context,
 				// understand the new BOLT 11 tagged field
 				// containing the blinded path, so we switch
 				// the bit to required.
-				v.Unset(lnwire.Bolt11BlindedPathsOptional)
-				v.Set(lnwire.Bolt11BlindedPathsRequired)
+				v = feature.SetBit(
+					v, lnwire.Bolt11BlindedPathsRequired,
+				)
 			}
 
 			return v