cni: Revert "cni: Use correct route MTU for various cloud cidrs"

The PR cilium#32244, that was merged with commit 29a340e, was intended to fix
IP fragmentation with WireGuard deployments, causing poor network
throughput and increased network latency. Unfortunately, after this PR
was merged, users began reporting issues with Cilium modifying the MTU
of the default interface of the node. This commit reverts the blamed
commit in an attempt to fix said issues.

The surfaced side-effect is tracked in issue cilium#33303.

Fixes: cilium#33258

Signed-off-by: Ryan Drew <ryan.drew@isovalent.com>

plugins/cilium-cni/cmd/interface.go

@@ -58,7 +58,7 @@ func interfaceAdd(ipConfig *current.IPConfig, ipam *models.IPAMAddressResponse,
 
 	if err := routingInfo.Configure(
 		ipConfig.Address.IP,
-		int(conf.RouteMTU),
+		int(conf.DeviceMTU),
 		conf.EgressMultiHomeIPRuleCompat,
 		false,
 	); err != nil {