If the flowid is available for the mbuf that finalised the creation
of a syncache connection, copy it into the inp_flowid field.

Without this, an incoming TCP connection won't have an inp_flowid marked
until some data comes in, and this means that things like the per-CPU
TCP timer option will choose a different CPU for the timer work.
(It also means that if one grabbed the flowid via an ioctl from userland,
it won't be available until some data has been received.)

Sponsored by:	Netflix, Inc.
There's actually no data in the PMU_GET_VERSION command.  Don't send any.
This change now allows the PMU to be used on PowerBook5,8.

MFC after:	1 week