Adds a filtering bitmask to DownloadStateCallback

Adds the ability for an EMBMS app to specify a filtering
bitmask to DownloadStateCallback, which is used to filter
out callbacks that the EMBMS app doesn't need to listen
to.

Test: Testapps
Change-Id: Id7f26ba3c3606c644b0ca3376df1107f5834facb
7 files changed