gve: Make gve_turn(up|down) ignore stopped queues

Currently the queues are either all live or all dead, toggling from one
state to the other via the ndo open and stop hooks. The future addition
of single-queue ndo hooks changes this, and thus gve_turnup and
gve_turndown should evolve to account for a state where some queues are
live and some aren't.

Tested-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Signed-off-by: Shailend Chand <shailend@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>