datapath/linux/ethtool: avoid leaking fd in ethtoolIoctl
datapath/linux/ethtool: avoid leaking fd in ethtoolIoctl

Close fd after using it to avoid leaking file descriptors.

Fixes: 2c878a512de9 ("cilium: auto-detect network interfaces for IPAMENI case")
Signed-off-by: Tobias Klauser <059b8b880f8441509ec8a65b50b4c6ae74ebea76@cilium.io>

michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,tgraf/cilium,cilium/cilium