Exit-node can't reach private network until private network subnets were advertised

### What is the issue?

After upgrading from 1.48.0 to 1.48.1, I found that I can't connect to my nas(192.168.123.118) by using exit-node function on my laptop(public network) via my server(192.168.123.24). And beyond that, I can't connect to my other VMs(located in 10.0.0.0/8 and 172.16.0.0/12) by using exit-node.
But I add an argument `--advertise-routes=192.168.123.118/32` on my server, the connection between my laptop and my nas resumed , although I didn't approve it on tailscale admin console. Under such circumstances, I can't connect to my home router(192.168.123.1), only my nas(192.168.123.118).
Later, I tried advertised all RFC1918 subsets on my server, all connections resumed.

### Steps to reproduce

ping node in private network from a device outside your private network which turn on exit-node function.

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

update 1.48.0 to 1.48.1

### OS

Linux, Windows

### OS version

Windows 11, Ubuntu 22.04

### Tailscale version

1.48.1

### Other software

none

### Bug report

BUG-68006623a61094290b49cab92484b56ab22fb0d4aa8c0536823e7e11835d2a10-20230825035318Z-e88b6df62bdf8264