mem: fix unmapping and marking segments as free

mem: fix unmapping and marking segments as free

Currently, page deallocation might fail if allocator cannot get page
fd, which will leave VA space still mapped, and will also not mark
page as free.

Fix page deallocation function to always unmap space before trying
to get rid of the page itself, and always mark page as free even if
page deallocation failed.

Fixes: a5ff05d60fc5 ("mem: support unmapping pages at runtime")
Fixes: 1a7dc2252f28 ("mem: revert to using flock and add per-segment lockfiles")

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>