get rid of needless use of NONEXISTENT_COOKIE which is simply 0

The random grab bag of stuff in BpfUtils.h is weird,
and I'm trying to trim it down.

Since this is coming from the kernel, 0 meaning error / no socket
is actually kernel api and thus guaranteed.

IMHO if (!cookie) is also clearer to read.

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I433dfca5695a04a42d632b7e0c2434db26c4ed00
2 files changed