ipcs: Avoid shmall overflows

ipcs: Avoid shmall overflows

Avoid computing the number of bytes in shmall, by only
computing and printing the number of Kbytes. This avoids
some overflows, e.g.

$ echo "4503599627370496" > /proc/sys/kernel/shmall
$ ipcs -l | grep 'max total shared memory'
Before:
max total shared memory (kbytes) = 18014398509481980
After:
max total shared memory (kbytes) = 18014398509481984

$ echo "99993599627370500" > /proc/sys/kernel/shmall
99993599627370500
$ ipcs -l | grep 'max total shared memory'
Before:
max total shared memory (kbytes) = 18014398509481980
After:
max total shared memory (kbytes) = 399974398509482000

v1->v2:
  Print the non-overflow KB value only for IPC_UNIT_KB and
IPC_UNIT_DEFAULT.
  This way --bytes and --human options will still get an expected
output
  (but not avoiding the overflow).

Signed-off-by: Vasilis Liaskovitis <vliaskovitis@suse.com>
Signed-off-by: Karel Zak <kzak@redhat.com>