Fix building without DoH support
This MR addresses the build issue with --disable-doh
that was
introduced by commit b69e7831 (part of
!6040 (merged)):
netmgr/netmgr.c:2657:1: error: no previous prototype for 'isc__nm_async_settlsctx' [-Werror=missing-prototypes]
2657 | isc__nm_async_settlsctx(isc__networker_t *worker, isc__netievent_t *ev0) {
| ^~~~~~~~~~~~~~~~~~~~~~~
It also tries to ensure we will catch similar issues immediately in the future (this particular problem was detected by pairwise testing, which is only run as part of scheduled pipelines and not before merging every MR).
We need this for September (BIND 9.19.5).
Closes #3508 (closed)