Setting a Tailscale Exit Node on MacOS breaks Internet Sharing

### What is the issue?

If you use Internet Sharing on MacOS, this allows using the Mac as a hotspot. However, when setting a Tailscale exit node, this kills the connection, as connected devices die on the second hop (from the client device to the gateway of the source connection). Connectivity does not return upon disconnecting the exit node, instead requiring turning Internet Sharing off and on again.

### Steps to reproduce

1. Setup internet sharing
2. Connect client device to Mac
3. Verify connectivity
4. Turn on Tailscale exit node
5. Verify lack of connectivity
6. Turn off Tailscale exit node
7. Verify lack of connectivity
8. Disconnect and reconnect client
9. Verify lack of connectivity

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

_No response_

### OS

macOS

### OS version

macOS Sequoia 15.3.1

### Tailscale version

1.82.0

### Other software

_No response_

### Bug report

BUG-214971acb3560b32c3b184feee6b8fa8248755ba495e4c6383f74fc0220cbcfb-20250418011508Z-82d79dcc9d4177a3