rfc6544: fix "Connection refused" error code

4463ed9e introduced a regression
and was checking for 70000+err instead of 120000+err.

Connection refused is 120111 (PJ_ERRNO_START_SYS + 111) and
not 70111 (PJ_ERRNO_START_STATUS + 111) leading to incorrect
error detection and some negotiation failed.

This patch also introduces some of the logs I used to debug this
issue that can be useful if a similar scenario come back.

Change-Id: I2a0e23f07f07ae81db14daea5d257976463c1133
GitLab: #438