app/testpmd: avoid pages being swapped out

app/testpmd: avoid pages being swapped out

Call the mlockall() function, to attempt to lock all of its process
memory into physical RAM, and preventing the kernel from paging any
of its memory to disk.

When using testpmd for performance testing, depending on the code path
taken, we see a couple of page faults in a row. These faults effect
the overall drop-rate of testpmd. On Linux the mlockall() call will
prefault all the pages of testpmd (and the DPDK libraries if linked
dynamically), even without LD_BIND_NOW.

Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Aaron Conole <aconole@redhat.com>
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>