nodemap: add validation to check that node map max is at least 16384.

This is the constant default size prior to adding the flag.
There's not much reason to lower this value so to avoid edge cases we'll just say that this is the lower bound.

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>

pkg/maps/nodemap/cell.go

@@ -4,6 +4,8 @@
 package nodemap
 
 import (
+	"fmt"
+
 	"github.com/cilium/cilium/pkg/bpf"
 	"github.com/cilium/cilium/pkg/hive/cell"
 	"github.com/spf13/pflag"
@@ -31,7 +33,11 @@ var defaultConfig = Config{
 	NodeMapMax: DefaultMaxEntries,
 }
 
-func newNodeMap(lifecycle cell.Lifecycle, conf Config) bpf.MapOut[Map] {
+func newNodeMap(lifecycle cell.Lifecycle, conf Config) (bpf.MapOut[Map], error) {
+	if conf.NodeMapMax < DefaultMaxEntries {
+		return bpf.MapOut[Map]{}, fmt.Errorf("creating node map: bpf-node-map-max cannot be less than %d (%d)",
+			DefaultMaxEntries, conf.NodeMapMax)
+	}
 	nodeMap := newMap(MapName, conf)
 
 	lifecycle.Append(cell.Hook{
@@ -43,5 +49,5 @@ func newNodeMap(lifecycle cell.Lifecycle, conf Config) bpf.MapOut[Map] {
 		},
 	})
 
-	return bpf.NewMapOut(Map(nodeMap))
+	return bpf.NewMapOut(Map(nodeMap)), nil
 }