Add a few more const refs

Add a few more const refs

In case of processPing we need to make a copy that potentially detaches
when masking is requested, but pings are < 125 bytes.
Before this code would copy the byte array in the same way much earlier.

Change-Id: If0592bb4b508eeb11fdbf05c4bb98b9679ed0549
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>