mempool: fix alignment of memzone length when populating

mempool: fix alignment of memzone length when populating

When populating a mempool with the default function, if there is not
enough virtually contiguous memory for the whole mempool, it will be
populated with several chunks. A chunk of the maximum available length
is requested with:

  mz = rte_memzone_reserve_aligned(..., len=0, ..., align=x)

If align is smaller than the page size, the address and the length of
the memzone may not be a multiple of the page size. This makes
rte_mempool_populate_virt() to fail because it requires them to be
page-aligned. This patch fixes that.

The problem can be reproduced easily by allocating more than available
memory:
  ./build/app/testpmd -l 0,1 -- --total-num-mbufs=65536
  ...
  Cause: Creation of mbuf pool for socket 0 failed: Invalid argument

After the patch, the error code is correct:
  ./build/app/testpmd -l 0,1 -- --total-num-mbufs=65536
  ...
  Cause: Creation of mbuf pool for socket 0 failed: Cannot allocate memory

Fixes: ba0009560c30 ("mempool: support new allocation methods")

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>