Tailscale writes ip 6 rules to main table leaving table 52 empty

### What is the issue?

Expect ip 6 rules to work much the same as ip 4.
Rules should be created to lookup table 52.
Instead, table 52 is empty and tailscale ip 6 rules are in the main table (254)

The impact is that one can't skip the tailscale rules by putting in an ip 6 rule with lower priority to lookup the main table - because although you can skip the lookup to table 52, the tailscale rules are in the main table and thus can't be skipped in this way.

### Steps to reproduce

Just install on an OpenWRT device.
I'm running the latest OpenWrt 23.05.2.

Examine output of these commands to see table 52 empty in ipv6:

ip -4 rule
ip -6 rule

ip -4 route show table 52
ip -6 route show table 52

ip -4 route show table main
ip -6 route show table main

### Are there any recent changes that introduced the issue?

no, I had not been looking closely at these rules before.

### OS

Linux

### OS version

OpenWrt 23.05.2

### Tailscale version

1.58.2

### Other software

_No response_

### Bug report

BUG-a66cd5332a343a4c721f058ad8d244806bcb0804e4248933c069519814810731-20240130031242Z-404c5627020b2690