[Fix] Regenerate DNS transaction ID before copying packet to TCP buffer

[Fix] Regenerate DNS transaction ID before copying packet to TCP buffer

When switching from UDP to TCP (e.g., on truncated response), the code
was copying the packet to the TCP output buffer before regenerating the
transaction ID to avoid collisions. This resulted in both UDP and TCP
packets having the same transaction ID.

Fix by moving the ID regeneration and IO channel switch logic before the
memcpy to the TCP output buffer, ensuring the TCP packet contains the
updated transaction ID.