Fix URI display in Leshan client log

[sbernard31]

trafficstars

Iv6 URI is not display correctly in log. [ ] is missing for Ipv6 : E.g. :

                 LeshanClient 2022-02-25 18:54:13,990 [INFO] Starting Leshan client ...
  CaliforniumEndpointsManager 2022-02-25 18:54:14,034 [INFO] New endpoint created for server coap://2a01:111:f100:9001:0:0:1761:93fa:5683 at coap://0.0.0.0:36680
                 LeshanClient 2022-02-25 18:54:14,036 [INFO] Leshan client[endpoint:mooky] started.
    DefaultRegistrationEngine 2022-02-25 18:54:14,037 [INFO] Trying to register to coap://2a01:111:f100:9001:0:0:1761:93fa:5683 ...
    DefaultRegistrationEngine 2022-02-25 18:54:14,122 [INFO] Registered with location '/rd/9IqAYK1ads'.
    DefaultRegistrationEngine 2022-02-25 18:54:14,123 [INFO] Next registration update to coap://2a01:111:f100:9001:0:0:1761:93fa:5683 in 53s...

See https://github.com/eclipse/leshan/issues/1210#issuecomment-1054100572