Add LoWPAN permissions to shell manifest

Without this change, `lowpanctl`, the command line tool for managing
LoWPAN networks, won't be able to work properly.

Cherry-picked from commit 1b730e4bd2c8e03d2a9bf041a4acd6fd6c0467f1.

Bug: b/65490659
Test: Manually
Change-Id: Ie44bac5c3bdc956dc2b1e79284ad18eae6931a32