NetBpfLoad: don't log the program failure buffer if it is empty

BPF_PROG_LOAD can fail with various permission related
errors, and then it doesn't provide any extra debug details.

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I9f6f0bf30158828fe31045a11a1f4c015feeb61e
1 file changed