Current Netlink message writer code relies on executing callbacks
with arbitrary data (pointer or integer) to flush the completed
messages.
This arbitrary data is stored as a union of { void *, uint64_t }.
At some stage, the message flushing code copied this data, using
direct uint64_t assignment instead of copying the union. It lead
to failure on CHERI, as sizeof(pointer) == 16 there.
Fix the code by making union non-anonymous and copying it entirely.
Reviewed by: br, jhb, jrtc27
Differential Revision: https://reviews.freebsd.org/D39557
MFC after: 2 weeks
9f324d8ac2