Add missing RequiresPermission to EthernetManager

The method requires NETWORK_STACK or MAINLINE_NETWORK_STACK permissions,
but the annotation was missing.

Test: m
Fixes: 150877670
Merged-In: I2af74cbcfa642f05f5e7bf85b2a8e8c38595f6ca
(cherry picked from commit e45d3ff8)

Change-Id: Ia215b74df99ae60be2e380917be68a272d658ef4