ANDROID: Increase x86 cmdline size to 4k

Recently we have started adding more things to kernel command line with
the new bootloader able to pass through crosvm built-in cmdline, and on
4.19 this causes problems because all bootconfig keys are also passed as
cmdline, exceeding the 2048 byte limit. This causes cmdline truncation
which dumps the device in recovery mode. Bump it up until we can turn
this testing down.

Bug: 217879977
Signed-off-by: Alistair Delva <adelva@google.com>
Change-Id: If341f72394de879d43da5206675d21683495d1d0