Updates the network cache of given networks.

Will add the networks in $networks to the cache. If network ID already exists
in the network cache then it will not be updated. The network is added to the
cache using the network group with the key using the ID of the networks.

function update_network_cache( $networks ) {
	$data = array();
	foreach ( (array) $networks as $network ) {
		$data[ $network->id ] = $network;
	}
	wp_cache_add_multiple( $data, 'networks' );
}