Add missing locks in dns_zone_getxfrsource4 et al. Addresses CID 468706, 468708, 468741, 468742, 468785, and 468778.
Cleanup dns_zone_setxfrsource4 et al to now return void.
Remove double copies with dns_zone_getprimaryaddr and dns_zone_getsourceaddr.
Closes #4933
Merge branch '4933-add-missing-locks-when-returning-addresses' into 'main'
See merge request isc-projects/bind9!9485