core.c: In core_build_tree, add missing log message for distribution node

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
core.c: Added combined node support in core_build_tree

Following combined node types are supported:
1. distribution & access
2. core & access

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
distrib.c: Add support for combined (access + distribution) node type

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
distrib/ibssa_opts.cfg: Add combined node_type (for access + distribution)

Signed-off-by: Hal Rosenstock <hal@mellanox.com>