Remove serde flatten for bgp parameters in external API

[rcgoodfellow]

Per this comment

#584 (comment)

This causes all of these fields to be duplicated in the progenitor client, which leads to some kinda painful duplication (e.g., https://github.com/oxidecomputer/omicron/blob/8186a1d914d4297136eb0892a3881a38dc9fc68b/sled-agent/src/bootstrap/early_networking.rs#L570-L605 and https://github.com/oxidecomputer/omicron/blob/8186a1d914d4297136eb0892a3881a38dc9fc68b/sled-agent/src/bootstrap/early_networking.rs#L617-L654).

maghemite/bgp/src/params.rs

Lines 156 to 165 in 715eed9

	/// Neighbor configuration with explicit per-address-family enablement (v3 API)
	#[derive(Debug, Deserialize, Serialize, JsonSchema, Clone, PartialEq)]
	pub struct Neighbor {
	pub asn: u32,
	pub name: String,
	pub group: String,
	pub host: SocketAddr,
	#[serde(flatten)]
	pub parameters: BgpPeerParameters,
	}