config: expose distinct accept-amp flag

This mirrors the accept-keysend flag, but also permits users to
eventually toggle off keysend separately from AMP.

server.go

@@ -427,6 +427,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		HtlcHoldDuration:            invoices.DefaultHtlcHoldDuration,
 		Clock:                       clock.NewDefaultClock(),
 		AcceptKeySend:               cfg.AcceptKeySend,
+		AcceptAMP:                   cfg.AcceptAMP,
 		GcCanceledInvoicesOnStartup: cfg.GcCanceledInvoicesOnStartup,
 		GcCanceledInvoicesOnTheFly:  cfg.GcCanceledInvoicesOnTheFly,
 		KeysendHoldTime:             cfg.KeysendHoldTime,