GitLab

 - not used function removed
 - DHCP6_HOOK_PACKET_RCVD_SKIP message typo fixed

- callouts called using HooksManager::callCallouts
- removed Dhcp6Srv::getServerHooks() and getHooksManager() declarations.
- updated sendPacket comment (reception->transmission)
- documented getCalloutHandle()
- indentation fixed for getSubnets6()

in D2 unit test.

Don't warn about static cast of function pointer print.

To silence cppcheck.

In particular, added a doUpdate version which supports TSIG. It is also
possible to specify Transport layer protocol preferred.

When logger initialization was disabled for a unit test, a few NULL pointer
assertions came up. This was because, some module commands were executed
without arguments (NULL pointer objects). NULL pointers were not checked
before logging arguments. This led to assertions. NULL pointers are now
checked and "(no arg)" string is logged if present.