nsc: Fix build problem if gtk config store is disabled

gtk config store pulled in libdl.so for us, so things fail
to link of the config store isn't enabled. This makes nsc
pull in libdl itself when its enabled.

src/internet-stack/wscript

@@ -105,3 +105,4 @@ def build(bld):
         obj.source.append ('nsc-tcp-l4-protocol.cc')
         obj.source.append ('nsc-tcp-socket-factory-impl.cc')
         obj.source.append ('nsc-sysctl.cc')
+        obj.uselib = 'DL'