stats: memory heap counters

stats: memory heap counters

- Add counters for the main-heap
- Add additional counters per heap:
  STAT_MEM_TOTAL
  STAT_MEM_USED,
  STAT_MEM_FREE,
  STAT_MEM_USED_MMAP,
  STAT_MEM_TOTAL_ALLOC,
  STAT_MEM_FREE_CHUNKS,
  STAT_MEM_RELEASABLE,

The per-heap counters are organised as a two dimensional vector.
total, used and free are directly available via symlinks.

vpp_get_stats ls "^/mem/"
/mem/stat segment
/mem/stat segment/total
/mem/stat segment/used
/mem/stat segment/free
/mem/main heap
/mem/main heap/total
/mem/main heap/used
/mem/main heap/free

vpp_get_stats dump "^/mem/main\ heap$"
[0 @ 0]: 1073741776 packets /mem/main heap
[1 @ 0]: 91586688 packets /mem/main heap
[2 @ 0]: 982155088 packets /mem/main heap
[3 @ 0]: 0 packets /mem/main heap
[4 @ 0]: 1073741776 packets /mem/main heap
[5 @ 0]: 433 packets /mem/main heap
[6 @ 0]: 981708688 packets /mem/main heap

Type: feature
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: I36725dde3b4b3befd27a8b4d3ba931f2d3b627cc