Revert "net/smc: Replace ib_query_gid with rdma_get_gid_attr"

This reverts commit ddb457c6.

The include rdma/ib_cache.h is kept, and we have to add a memset
to the compat wrapper to avoid compiler warnings in gcc-7

This revert is done to avoid extensive merge conflicts with SMC
changes in netdev during the 4.19 merge window.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>