__u8 is not available on FreeBSD so use u_int8_t instead

tvheadend-3.4/src/dvb/diseqc.h:10: error: expected declaration specifiers or '...' before '__u8'
tvheadend-3.4/src/dvb/diseqc.h:11: error: expected declaration specifiers or '...' before '__u8'
Fix IPv4 multicasting on FreeBSD and make IPv6 multicasting optional
because it's not yet supported on FreeBSD.
Add kqueue support and make epoll optional.
Add kqueue support and make epoll optional.