build: Drop syslog on DISABLE_NET_TESTS=1

Even if local, it requires communication with a daemon
which may not be available.  This is creating problems
for getting an Ubuntu package going in Launchpad's PPA.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/3989062

src/pkg/Makefile

@@ -187,7 +187,7 @@ NOBENCH=\
 
 # Disable tests that depend on an external network.
 ifeq ($(DISABLE_NET_TESTS),1)
-NOTEST+=http net
+NOTEST+=http net syslog
 endif
 
 # Disable tests that windows cannot run yet.