cs.c: install format specifier for %F

This makes the debug output usable:
CS:Twalk tag 1d fid 21 newfid 24 nwname 1 0:cs CS:Rwalk tag 1d nwqid 1d 0:(0000000000000001x 2d )  22CS:Job done
CS:Topen tag 1d fid 24d mode 2CS:Ropen tag 1d qid (0000000000000001x 2d ) iounit 0d  24CS:Job done
CS:Twrite tag 1d fid 24 offset 0 count 17d 'tcp!localhost!ssh'CS:write tcp!localhost!sshCS:Rwrite tag 1d count 17d 11CS:Job done
CS:Tread tag 1d fid 24 offset 0 count 127dCS:Rread tag 1d count 27d '/net/tcp/clone 127.0.0.1!22' 38CS:Job done
CS:Tread tag 1d fid 24 offset 27 count 127dCS:Rread tag 1d count 0d <no data> 11CS:Job done
CS:Tclunk tag 1d fid 24dCS:Rclunk tag 1d 7CS:Job done

This shows where we could make things better: an addition to the protocol, namely, Treadfile, would reduce this overhead
from 6 packets to 1.

And if we could make that a top-level system call, well ...

Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>