stack: fix reload head when pop fails

stack: fix reload head when pop fails

The previous commit 18effad9cfa7 ("stack: reload head when pop fails")
only changed C11 implementation, not generic implementation.

List head must be loaded right before continue (when failed to find the
new head). Without this, one thread might keep trying and failing to pop
items without ever loading the new correct head.

Fixes: 3340202f5954 ("stack: add lock-free implementation")
Cc: stable@dpdk.org
Signed-off-by: Julien Meunier <julien.meunier@nokia.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>