ashmem: Test for ASHMEM_GET_SIZE for ashmem-memfd compatibility

ASHMEM_SET_SIZE will return  an error in the ashmem-memfd compatibility
logic, but ASHMEM_GET_SIZE will work as expected, so exercise that ioctl
command when testing for ashmem-memfd compatibility.

Bug: 111903542
Change-Id: I3a042063082fdf6d8d836ad9b37becc318e8d89d
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>