if_clone: don't overwrite dump_nl of drivers

[pouria]

Summary

if_clone: don't overwrite dump_nl of drivers with default.
required by D54172.

Test Plan

The only existing interface driver that uses nl_dump is if_vlan,
and there no user for its nl_dump. ifconfig uses ioctl for if_vlan.
To test status functionality of ifconfig vlan:

ifconfig epair0 create up
jail -c persist name=nlvnet1 mount.devfs devfs_ruleset=5 vnet
vnet.interface=epair0b path=/
ifconfig -j nlvnet1 epair0b up
ifconfig vlan0 create inet6 2001:db8::1 vlan 10 vlandev epair0a
ifconfig -j nlvnet1 vlan0