Floating IP create by non-admin fails when pool is specified

[david-crespo]

This permission check fails when the pool is specified. I think we should check a different permission, but it's conceivable we should instead change the permissions on this resource.

omicron/nexus/src/app/external_ip.rs

Lines 114 to 122 in 9123e4b

	let pool = match pool {
	Some(pool) => Some(
	self.ip_pool_lookup(opctx, &pool)?
	.lookup_for(authz::Action::Read)
	.await?
	.0,
	),
	None => None,
	};