Change eos BGP_PREFIX_THRESH_EXCEEDED error
Change eos BGP_PREFIX_THRESH_EXCEEDED error

The error `BGP_PREFIX_THRESH_EXCEEDED` under `eos` should be
`BGP_PREFIX_LIMIT_EXCEEDED`. This is because the message listed only
occurs after the limit has been exceeded.

napalm-automation/napalm-logs,napalm-automation/napalm-logs