Quick patch for error when writing mem.lim default

When writing the system default for memory.limit_in_bytes (which is a LLONG_MAX)
the write fails. The number is equivalent to -1 (unlimited). So during dump,
store the number -1 instead.

Change-Id: Iafccc96bf5dbade763d7addaeda24194616e4d5f
Signed-off-by: Garrison Bellack <gbellack@google.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>