cmd/derper: apply TCP keepalive and timeout to TLS as well

I missed a case in the earlier patch, and so we're still sending 15s TCP
keepalive for TLS connections, now adjusted there too.

Updates tailscale/corp#17587
Updates #3363

Signed-off-by: James Tucker <james@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f