DroidSec: Check sscanf returns in function iw_set_priv

In the two clauses "powermode" and "CONFIG-TX-TRACKING",
it should be confirmed that cmd_len is greater than amount
incrementing cmd when form ptr,and must check return from
sscanf to confirm that parameters were parsed correctly
before subsequent use.

Change-Id: I9e93c3f34b116f6fac1bd81f32956fb88cba807a
CRs-fixed: 554538