Replace deprecated IO::Socket::INET6 with IO::Socket::IP.

In the sendsyslog-dropped test the client has to write a log message
before syslogd is running. To fix a race in regress, delay the
syslogd startup until the message has been written. For debugging

In the sendsyslog-dropped test the client has to write a log message
before syslogd is running. To fix a race in regress, delay the
syslogd startup until the message has been written. For debugging
add the process class to all die messages.

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Test what happens when syslogd reaches its file descriptor limit
and cannot accept TCP connections anymore.