dumpconfig produces invalid NAT toml

[corverroos]

System information

Geth version: v1.15.1

Expected behaviour

v1.15.0 added support to configuring Node.P2P.NAT in config.toml.

Given a config.toml with a NAT value configured, one expects that geth dumpconfig would produce valid toml with the same NAT configured.

Actual behaviour

It produces invalid toml that cannot be used a config.

Steps to reproduce the behaviour

config.toml:

[Node.P2P]
NAT = "extip:1.2.3.4"

Run dumpconfig:

docker run --volume=./config.toml:/tmp/config.toml ethereum/client-go:v1.15.1 dumpconfig --config=/tmp/config.toml

Produces invalid toml that contains:

[Node.P2P.NAT]
Interface = "extip:1.2.3.4"

Note that running dumpconfig with legacy --nat=expip:1.2.3.4 cli flag the output is correct.