test: don't run fixedbugs/issue11656.go on netbsd/386

The netbsd/386 builder reports a failure at
http://build.golang.org/log/c21c45a4fc6f4845868aa3ebde0f5bb3f167f3a3

I'm assuming that this is similar to the unknown openbsd failure.

Update #11910.

Change-Id: I9cdfefa23dc7cda3849f14814b3ce531f1d39e93
Reviewed-on: https://go-review.googlesource.com/12777Reviewed-by: David Crawshaw <crawshaw@golang.org>

test/fixedbugs/issue11656.go

@@ -8,8 +8,9 @@
 // it manages to invoke the signal handler, so this test fails there.
 // +build !darwin !386
 //
-// openbsd/386 and plan9/386 don't work, not sure why.
+// openbsd/386, netbsd/386, and plan9/386 don't work, not sure why.
 // +build !openbsd !386
+// +build !netbsd !386
 // +build !plan9 !386
 //
 // windows doesn't work, because Windows exception handling