Add check for the port when specifying an endpoint

When specifying an endpoint with -p/--peer, we could mistaken with the domain name. In that case we will get an error. But, if we mistake with the port, we don’t get the information that something is wrong. We should add back this feature.

Code at 0.6.1 state https://git.duniter.org/clients/python/silkaj/blob/f44bd679f00c95addca7dd827991c8bbaa2b84e4/silkaj/network_tools.py#L190

#113 (closed): 9) "I think the last port is 65535"