hyperv: Fix a compiler warning in netvsc_send()

Fixed: warning: cast from pointer to integer of different size

The Hyper-V hosts always use 64 bit request id. The guests can have 32 or 64
bit pointers which equal to the ulong type size. So we cast it to ulong type.
And, assigning 32bit integer to 64 bit variable works fine.

The VMBus returns the same id in the completion packet. But the value has no
effect on the host side.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>