mem: set fd to -1 for anonymous mmap

mem: set fd to -1 for anonymous mmap

https://dpdk.org/tracker/show_bug.cgi?id=18

Indicated that several mmap call sites in the [linux|bsd]app eal code
set fd that was not -1 in their calls while using MAP_ANONYMOUS.  While
probably not a huge deal, the man page does say the fd should be -1 for
portability, as some implementations don't ignore fd as they should for
MAP_ANONYMOUS.

Suggested-by: Solal Pirelli <solal.pirelli@gmail.com>
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>