kqueue: Define older kqueue event types better

struct kqueue is designed to live in a restricted namespace, but the
older compat versions are not. Shift to using unsigned short instead
of u_short, unsigned int instead of u_int and the __*int*_t types
instead of the unprefiexed versions.

Sponsored by: Netflix
Reviewed by: brooks
Differential Revision: https://reviews.freebsd.org/D33056