Restored the Linux port mutex retryv6.4.1_cert

This was reverted because a NetX Secure regression test segfaulted with it
in place. The cause was the test: it hands the certificate verify path a
stack-local certificate whose signature it never assigns, and this change
moves the stack layout that decides whether the unassigned slot reads null
or a readable leftover. That test has been fixed, so the retry comes back.

Measured with the test unfixed and this change in place, on a layout built
without the stack protector: eight of eight runs segfault, the fault read
from the faulting process as a null signature dereferenced by the ECDSA
verify. With the test fixed, nineteen build configurations run it eight
times each with no fault.

Without this change, a thread signalled into the port's suspend handler
never returns to the contended-mutex loop, the next unlock's wake-up is
lost, the scheduler is left parked, and the timer interrupt never runs --
which stalls the tick and hangs about 0.39% of instances of a few TCP
tests for their full timeout.

0 files changed, 0 insertions, 0 deletions