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).

docs/release-notes/release-notes-0.19.0.md

@@ -27,6 +27,10 @@
   cause a nil pointer dereference during the probing of a payment request that 
   does not contain a payment address.
 
+* [Use the required route blinding 
+  feature-bit](https://github.com/lightningnetwork/lnd/pull/9143) for invoices 
+  containing blinded paths.
+
 # New Features
 ## Functional Enhancements
 ## RPC Additions

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