eth, core: terminate the downloader immediately when shutdown signal is received

[jsvisa]

closes #32058

Test with the hoodi testnet in full-sync, the results as below

master branch about 36seconds

INFO [06-18|15:08:01.553] Got interrupt, shutting down...
INFO [06-18|15:08:01.553] HTTP server stopped                      endpoint=[::]:4545
INFO [06-18|15:08:01.553] HTTP server stopped                      endpoint=[::]:4546
INFO [06-18|15:08:01.553] HTTP server stopped                      endpoint=[::]:8551
INFO [06-18|15:08:01.553] IPC endpoint closed                      url=/data/geth.ipc
... 
INFO [06-18|15:08:37.213] Blockchain stopped

this branch about 5seconds

INFO [06-18|15:05:20.774] Got interrupt, shutting down...
INFO [06-18|15:05:20.774] HTTP server stopped                      endpoint=[::]:4545
INFO [06-18|15:05:20.774] HTTP server stopped                      endpoint=[::]:4546
INFO [06-18|15:05:20.774] HTTP server stopped                      endpoint=[::]:8551
INFO [06-18|15:05:20.774] IPC endpoint closed                      url=/data/geth.ipc
...
INFO [06-18|15:05:25.462] Blockchain stopped

[s1na]

Confirming this should also fix #31508??

[rjl493456442]

Not sure. The hang after initial synchronization might be relevant with something else.