libusb: refactor the process of setting option when init the context.

From
https://github.com/libusb/libusb/commit/6622f386f52807dac76c8a260c98aa02c311bc93#diff-c1f9bc250077d41456a3e580fca0ddf5d8c25b741bff6d9b9505990a8b70b254R2358.
We are able to set all of the option from the init_context. To address
this, we modify the process of setting option in init_context to make it be more clear and then
adapat libusb_set_option inside to all other option.

Reviewed by: adrian
Sponsored By: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D51224