misc: add gdb macros

misc: add gdb macros

These gdb macros should prove very helpul when poking around in core files.

Pifi (pool_is_free_index) is not straighforward. Best to work it out
once.

Others:
 bitmap_get = clib_bitmap_get
 vl = vec_len
 pe = pool_elts
 node_name_from_index, as described
 vnet_buffer_opaque, prints the primary buffer opaque
 vnet_buffer_opaque2, prints the secondary buffer opaque

Fix vppinfra unit-test compile error

Type: improvement
Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: Id2a2391a47e5a07cf3757f473e3805cc04784161