Security Fix: Crafted GATT request causes BT stack crash

A while loop and condition check for the value of a type to be 0
when in fact since the value.len is arbitrary it could make the
remaining length "less than 0" and since the type is unsigned it'll
never be "less than 0."

Use signed type for loop and conditional checking.

Additionally, make sure the value.len when used to read an array is not
more than the remaining length of the data.

Bug: 197536150
Test: poc application
Tag: #security
Change-Id: I20d66ddd1055577d7d39aba447233c19081bb789