UCT/IB/ROCE: Use ipv6 non link-local GID in priority

[tvegas1]

What?

When selecting RoCE GID, search for IPv6 non link-local before trying to use IPv6 link-local GID.

Why?

Some clusters only have gid_index=3 usable. Manually setting UCX_IB_GID_INDEX=3 is cumbersome and error-prone.

How?

Relevant cli: show_gids. Tested on two clusters:

UCX_LOG_LEVEL=debug ./rfs/bin/ucx_perftest -l -t ucp_put_bw | grep gid_index

# For all interfaces (mlx5_x/roce_railsx):
UCX_NET_DEVICES=mlx5_0:1 UCX_PROTO_INFO=y ./rfs/bin/ucx_perftest -l -t ucp_put_bw
UCX_NET_DEVICES=mlx5_0:1 UCX_PROTO_INFO=y ./rfs/bin/ucx_perftest -t ucp_put_bw remote-node

[brminich]

@amastbaum, @yosefe - can you re-approve pls?