travis: extend race detection for swarm p2p packages (#19287)

* travis: remove verbose from Swarm race tests

By removing -v our output will be cleaner, but the Travis job still
won't be terminated - due to 'no output for 10 minutes' - as keepalive
.sh produces a log line every 5 minutes.

* travis: extend Swarm race detection to p2p subpackages

As p2p/protocols, p2p/simulations and p2p/testing packages mostly
belong to the Swarm team.

.travis.yml

@@ -232,4 +232,4 @@ matrix:
       go: 1.12.x
       git:
         submodules: false # avoid cloning ethereum/tests
-      script: ./build/travis_keepalive.sh go test -v -timeout 20m -race ./swarm...
+      script: ./build/travis_keepalive.sh go test -timeout 20m -race ./swarm... ./p2p/{protocols,simulations,testing}/...