Query GID Attributes

Query GID attributes, such as GID type.

• ibv_exp_query_gid_attr

GID type can be extracted from the ibsysfs.

Review ibv_query_gid_type, ibv_read_sysfs_file from rdma-core:
https://github.com/linux-rdma/rdma-core/blob/master/libibverbs/verbs.c