mem: fix freeing segments in --huge-unlink mode

mem: fix freeing segments in --huge-unlink mode

When using huge_unlink we unlink the segment right
after allocation. Although we unlink the file we keep
the fd in fd_list so file still exist just the path deleted.
When freeing the hugepage we need to close the fd and assign
it with (-1) in fd_list for the page to be released.

The current flow fails rte_malloc in the following flow when working
with --huge-unlink option:
1. alloc_seg() for segment A -
    We allocate a segment, unlink the path to the segment
    and keep the file descriptor in fd_list.
2. free_seg() for segment A -
    We clear the segment metadata and return - without closing fd
    or assigning (-1) in fd list.
3. alloc_seg() for segment A again -
    We find segment A as available, try to allocate it,
    find the old fd in fd_list try to unlink it
    as part of alloc_seg() but failed because path doesn't exist.

The impact of such error is falsely failing rte_malloc()
although we have hugepages available.

Fixes: d435aad37da7 ("mem: support --huge-unlink mode")
Cc: stable@dpdk.org
Signed-off-by: Roy Shterman <roy.shterman@vastdata.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>