Ligato code does NOT work with external .yaml file, because of this:
//
	func (plugin *Plugin) applyExternalConfig() {
	var externalCfg *config.Bgp
	found, err := plugin.PluginConfig.GetValue(externalCfg)
//
The above code (line 70) defined externalCfg of pointer type and passed it as-is in PluginConfig.GetValue(externalCfg) in line 71. That meant passing a different memory address from where the external file really was (remember, every time a variable is passed as parameter, a new copy of the variable is created), resulting in a garbage being passed to ParseConfigFromYamlFile function inside p.GetConfigName(), which then returned an error.

Instead, define config.Bgp variable as a pointer to the address where the external .yaml file is, and pass the same pointer in PluginConfig.GetValue(externalCfg) in line 71. 
https://gobyexample.com/pointers
http://goinbigdata.com/golang-pass-by-pointer-vs-pass-by-value/

Signed-off-by: Rajiv Asati <rajiva@cisco.com>

Ligato BGP code fails if used with an external .yaml file, because line 70 defined externalCfg of pointer type and passed it as-is in PluginConfig.GetValue() in line 71, as shown below:
//
	func (plugin *Plugin) applyExternalConfig() {
	var externalCfg *config.Bgp
	found, err := plugin.PluginConfig.GetValue(externalCfg)
//
The above meant passing a different memory address from where the external file really was (remember, every time a variable is passed as parameter, a new copy of the variable is created), resulting in a garbage being passed to ParseConfigFromYamlFile() function inside p.GetConfigName(), which then returned an error.

Fix is to define config.Bgp variable as a pointer to the address where the external .yaml file is, and pass the same pointer in PluginConfig.GetValue() in line 71 and 80. 

https://gobyexample.com/pointers
http://goinbigdata.com/golang-pass-by-pointer-vs-pass-by-value/