tbf: add llc_queue_size() to check llc_queue is valid before calling size()

gcc6 is optimizing if (!this) {CODE} as this is assumed to never be a
std::nullptr here. Move the null check to the caller. In preparation of
removing the check within llc_queue->size(), all callers must check the object
before calling it. Make sure of that: make the llc_queue() access function
protected and offer only a public llc_queue_size() function that incorporates
the NULL check. All current callers are only interested in the
llc_queue_size().

Tweaked-by: nhofmeyr
Change-Id: I88cc3180f8f86785e3f07981895dabddf50b60a2
3 files changed