Harmonize vec/pool_get_aligned object sizes and alignment requests

Harmonize vec/pool_get_aligned object sizes and alignment requests

Object sizes must evenly divide alignment requests, or vice
versa. Otherwise, only the first object will be aligned as
requested.

Three choices: add CLIB_CACHE_LINE_ALIGN_MARK(align_me) at
the end of structures, manually pad to an even divisor or multiple of
the alignment request, or use plain vectors/pools.

static assert for enforcement.

Change-Id: I41aa6ff1a58267301d32aaf4b9cd24678ac1c147
Signed-off-by: Dave Barach <dbarach@cisco.com>