vppinfra: bihash improvements

Template instances can allocate BIHASH_KVP_PER_PAGE data records
tangent to the bucket, to remove a dependent read / prefetch.

Template instances can ask for immediate memory allocation, to avoid
several branches in the lookup path.

Clean up l2 fib, gpb plugin codes: use clib_bihash_get_bucket(...)

Use hugepages for bihash allocation arenas

Type: improvement

Signed-off-by: Dave Barach <dave@barachs.net>
Signed-off-by: Damjan Marion <damarion@cisco.com>
Change-Id: I92fc11bc58e48d84e2d61f44580916dd1c56361c