RDMA/rxe: Replace netdev dev addr with raw_gid

Because TUN device does not have dev_addr, but a gid in rdma is needed,
as such, a raw_gid is generated to act as the gid. The similar commit is
in SIW. This commit learns from the similar commit bad5b6e3
("RDMA/siw: Fabricate a GID on tun and loopback devices") in SIW.

Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Link: https://patch.msgid.link/20250119172831.3123110-2-yanjun.zhu@linux.dev


Signed-off-by: Leon Romanovsky <leon@kernel.org>