Fixes bug where the app callback was getting the length of the status
request transfer rather than the length of the data stage payload.
TODO: Right now this returns the expected length, when it really should
be returning the transfer length.
Adds configuration option CFG_TUSB_ALT_BIT_PACKING_ALIGNMENT, which
substitutes bitfield variable " : 0" padding syntax with an unused
variable of size equal to the remaining number of bits.
This change resolves aligned access issues for some platforms.
Default behavior is original if the option is not explicitly enabled.