vppinfra: add heap header in front of dlmalloc space

vppinfra: add heap header in front of dlmalloc space

This patch adds smal header in front of dlmalloc space, and it stores
some additional information about the heap.

Immediate benefit of this patch is that we know the underlying page size
si we can display heap page statistics / real memory usage.

Type: improvement
Change-Id: Ibd6989cc2f2f64630ab08734c9552e15029c5f3f
Signed-off-by: Damjan Marion <[email protected]>