IB/core: Make ib_addr a core IB module

IP based addressing introduces the usage of rdma_addr_find_dmac_by_grh()
within ib_core.  Since this function is declared in ib_addr, ib_addr
should be a part of the core INFINIBAND modules, rather than
INFINIBAND_ADDR_TRANS.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>