Terrible performance (packet loss) with Mullvad exit node enabled

### What is the issue?

With local (in-country) Mullvad exit node enabled:

```
% ping -c5 quad9.net
PING quad9.net (195.176.255.138): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
64 bytes from 195.176.255.138: icmp_seq=2 ttl=57 time=120.069 ms
64 bytes from 195.176.255.138: icmp_seq=3 ttl=57 time=119.576 ms
64 bytes from 195.176.255.138: icmp_seq=4 ttl=57 time=119.955 ms

--- quad9.net ping statistics ---
5 packets transmitted, 3 packets received, 40.0% packet loss
round-trip min/avg/max/stddev = 119.576/119.867/120.069/0.211 ms
```

With Mullvad exit node disabled:
```
% ping -c5 quad9.net
PING quad9.net (195.176.255.138): 56 data bytes
64 bytes from 195.176.255.138: icmp_seq=0 ttl=51 time=26.557 ms
64 bytes from 195.176.255.138: icmp_seq=1 ttl=51 time=26.606 ms
64 bytes from 195.176.255.138: icmp_seq=2 ttl=51 time=26.867 ms
64 bytes from 195.176.255.138: icmp_seq=3 ttl=51 time=26.588 ms
64 bytes from 195.176.255.138: icmp_seq=4 ttl=51 time=26.473 ms

--- quad9.net ping statistics ---
5 packets transmitted, 5 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 26.473/26.618/26.867/0.133 ms
```

It is intermittent in nature.

### Steps to reproduce

_No response_

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

Not sure, maybe to do with the 1.94.1 update possibly. But not 100% certain.

### OS

macOS

### OS version

Tahoe 26.2

### Tailscale version

1.94.1 (app store)

### Other software

_No response_