ovs: ability to set other-config on bridge

I see that we can only set openflow protocols as bridge options.
```golang
// Bridge sets configuration for a bridge using the values from a BridgeOptions
// struct.
func (v *VSwitchSetService) Bridge(bridge string, options BridgeOptions) error {
// Prepend command line arguments before expanding options slice
// and appending it
args := []string{"set", "bridge", bridge}
args = append(args, options.slice()...)
log.Println(args)
_, err := v.v.exec(args...)
return err
}
```
Would it be possible to add another method to allow for setting something like "other-config:forward-bpdu=true", or possibly extend the BridgeOptions struct to allow 'other-options'

```golang
// BridgeOther allows for setting of non openflow BridgeOptions
func (v *VSwitchSetService) BridgeOther(bridge string, options string) error {
// Prepend command line arguments before expanding options string
// and appending it
args := []string{"set", "bridge", bridge}
args = append(args, options)
_, err := v.v.exec(args...)
return err
}
```
Thanks!