timers: no need to clear keepalive in persistent keepalive

timers: no need to clear keepalive in persistent keepalive

We do this after sending the keepalive anyway.

This is something of a regression, though, since before we'd cancel and
then send, but now we send and then cancel, so it introduces a potential
race, but hopefully that isn't too big of a deal.

Kernel module commit a24b3e6e15ae1ea1291666e5da910caf43eedbaf