mem: do not unmap overlapping region on mmap failure

mem: do not unmap overlapping region on mmap failure

This isn't documented in the manuals, but a failed
mmap(..., MAP_FIXED) may still unmap overlapping
regions. In such case, we need to remap these regions
back into our address space to ensure mem contiguity.
We do it unconditionally now on mmap failure just to
be safe.

Verified on Linux 4.9.0-4-amd64. I was getting
ENOMEM when trying to map hugetlbfs with no space
left, and the previous anonymous mapping was still
being removed.

Fixes: 582bed1e1d1d ("mem: support mapping hugepages at runtime")
Cc: stable@dpdk.org
Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>