gve: Add adminq mutex lock

gve: Add adminq mutex lock

We were depending on the rtnl_lock to make sure there is only one adminq
command running at a time. But some commands may take too long to hold
the rtnl_lock, such as the upcoming flow steering operations. For such
situations, it can temporarily drop the rtnl_lock, and replace it for
these operations with a new adminq lock, which can ensure the adminq
command execution to be thread-safe.

Signed-off-by: Ziwei Xiao <ziweixiao@google.com>
Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20240625001232.1476315-2-ziweixiao@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>