MacOS: Silence pipe error in set_interface_alt_setting()

MacOS: Silence pipe error in set_interface_alt_setting()

darwin_set_interface_altsetting() no longer returns the status of the underlying SetAlternateInterface(), but instead the result of a subsequent GetNumEndpoints() call. This reverts to the behaviour prior to commit 065e586.

Since darwin_set_interface_altsetting() resets the interface after SetAlternateInterface(), one of the consequences is that if SetAlternateInterface() returns a kIOUSBPipeStalled error, and the interface is successfully reset, darwin_set_interface_altsetting() now returns LIBUSB_SUCCESS instead of LIBUSB_ERROR_PIPE.

Closes: #838

Signed-off-by: Freek Dijkstra
Signed-off-by: Nathan Hjelm <hjelmn@google.com>