Use atomics on couple of ADB entry members (.srtt, .flags, .expires, and .lastage) to remove ADB entry locking from couple of hot spots. The most prominent place is copy_namehook_lists() that gets called under ADB name lock and if the namehook list is long it acquires-releases quite a few ADB entry locks. Changing those ADB entry members to atomics allowed us to new_adbaddrinfo() not require locked ADB entry and since adbentry_overquota() already used atomics and handling lame information was dropped in the previous commit, we could not make the copy_namehook_lists() lockless.
The other hotspot is dns_adb_adjustsrtt() and dns_adb_agesrtt() that can now use atomics because .srtt is already atomic_uint.
And the last place that could now use atomics is dns_adb_changeflags().
This doesn't closes #4326 (closed) as there's more stuff to do.