p2p/protocols: fix data race in TestProtocolHook (#19242)

dummyHook's fields were concurrently written by nodes and read by
the test. The simplest solution is to protect all fields with a mutex.

Enable: TestMultiplePeersDropSelf, TestMultiplePeersDropOther as they
seemingly accidentally stayed disabled during a refactor/rewrite
since 1836366a.

resolves ethersphere/go-ethereum#1286