ctld: Add missing initializers for several class members

These fields all need to be explicitly initialized with zeroes. Prior
to the conversion to C++ these fields were zeroed by calloc().

This worked for me in earlier testing as my test boxes had
MALLOC_PRODUCTION enabled in make.conf.

PR: 289115
Reported by: Slawa Olhovchenkov <slw zxy.spb.ru>
Fixes: eb0dc901a541 ("ctld: Convert struct auth_group to a C++ class")
Fixes: 6acc7afa34aa ("ctld: Convert struct port to a hierarchy of C++ classes")
Fixes: 2bb9180bb5d0 ("ctld: Convert struct target to a C++ class")
Fixes: ed076901ec80 ("ctld: Convert struct ctld_connection to a C++ class")
Sponsored by: Chelsio Communications