kqueue: fix conversion of timer data to sbintime

This unbreaks the i386 kqueue timer tests after a recent change switched
NOTE_ABSTIME over to using microseconds. Notably, the data argument (which
holds useconds) is an int64_t, but we were passing it to timer2sbintime
which takes an intptr_t. Perhaps in a previous incarnation, intptr_t would
have made sense, but now it just leads to the timestamp getting truncated
and subsequently rejected when it no longer fits in an intptr_t.

PR: 245768
Reported by: lwhsu / CI
MFC after: 1 week