3ed12b6fd9
Control transfers can transfer less than was requested by the host in the wLength field. if this short transfer is a multiple of the endpoint's packet size, a zero length packet must be sent. Adds tests for a range of control transfer IN requests, and properly supports this in the core. Based heavily on work by Kuldeep Dhaka. See https://github.com/libopencm3/libopencm3/pull/505 and https://github.com/libopencm3/libopencm3/pull/194 for original discussion. Tested with stm32f4, stm32f103 and stm32l053.