ipn/ipnlocal: deduplicate RoutableIPs / RequestTags in hostinfo (#20759)

Both RoutableIPs and RequestTags act as a set of values. There have been
cases of misconfigured IAC populating duplicate values, resulting in
more data being sent to control than needs to be.

Updates tailscale/corp#44607

Signed-off-by: Evan Lowry <evan@tailscale.com>