hv_netvsc: Print value of invalid ID in netvsc_send_{completion,tx_complete}()

That being useful for debugging purposes.

Notice that the packet descriptor is in "private" guest memory, so
that Hyper-V can not tamper with it.

While at it, remove two unnecessary u64-casts.

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>