xv6/mkfs.c: bump the number of inodes to 4000
xv6/mkfs.c: bump the number of inodes to 4000

necessary to run smallfile on xv6fs

fscq turns out to be REALLY slow compared to xv6fs on smallfile:

  xv6fs:

    nickolai@mojave:~/proj/fscq/bench/LFStest$ ./smallfile 500 10 /tmp/ft/
    ./smallfile 500 10 /tmp/ft/
    ./smallfile: creat took 60343 usec
    ./smallfile: read took 21145 usec
    ./smallfile: unlink took 16083 usec

  fscq:

    nickolai@mojave:~/proj/fscq/bench/LFStest$ ./smallfile 500 10 /tmp/ft/
    ./smallfile 500 10 /tmp/ft/
    ./smallfile: creat took 2338208 usec
    ./smallfile: read took 925935 usec
    ./smallfile: unlink took 661408 usec

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl