Disable "tun" package tests on TravisCI

.travis.yml

@@ -14,6 +14,7 @@ script:
 - go test -race -v ./common/osl
 - go test -race -v ./common/protocol
 # TODO: enable once known race condition is addressed
+#       also, see comment below
 #- sudo -E env "PATH=$PATH" go test -race -v ./common/tun
 - go test -race -v ./transferstats
 - go test -race -v ./server
@@ -22,7 +23,11 @@ script:
 - go test -v -covermode=count -coverprofile=common.coverprofile ./common
 - go test -v -covermode=count -coverprofile=osl.coverprofile ./common/osl
 - go test -v -covermode=count -coverprofile=protocol.coverprofile ./common/protocol
-- sudo -E env "PATH=$PATH" go test -v -covermode=count -coverprofile=tun.coverprofile ./common/tun
+# TODO: fix and reenable test, which is failing in TravisCI environment:
+# --- FAIL: TestTunneledTCPIPv4
+#    tun_test.go:226: startTestTCPClient failed: syscall.Connect failed: connection timed out
+#
+#- sudo -E env "PATH=$PATH" go test -v -covermode=count -coverprofile=tun.coverprofile ./common/tun
 - go test -v -covermode=count -coverprofile=transferstats.coverprofile ./transferstats
 - go test -v -covermode=count -coverprofile=server.coverprofile ./server
 - go test -v -covermode=count -coverprofile=psinet.coverprofile ./server/psinet