Set initial meta state to AMETA_NONE

Currently, the default meta state is AMETA_NUM_LOCK_ON, that may cause
some keyboard such as Apple Wireless Keyboard send the mismatched keys.

Ideally, if the keyboard didn't contain the led key, it should not
handle such key to change any state, this CL temporarily set the
initialied state to none to prevent some unexpected behavior when
user connected a new keyboard.

Bug: 194465459
Test: atest inputflinger_tests
Change-Id: Iad9fc01d16444e7d40a704678d3d27cdd110765c