Fix mobile signal icon when in airplane mode

1. Empty state was drawing a line too thing and not dark enough to be
seen.
2. Airplane mode should be the slashed, full signal, not the
empty one

Going into airplane mode now draws the full signal, lighter than normal,
with a slash. And the empty state now has a thicker line.

Test: runtest systemui
Fixes: 62794461
Change-Id: Ic5e40d2e0f6ebe0d270129f10883a1fcb146d717