[9.18] fix: dev: Add missing locks when returning addresses

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

Backport of MR !9485

Merge branch 'backport-4933-add-missing-locks-when-returning-addresses-9.18' into 'bind-9.18'

See merge request isc-projects/bind9!10260