MidiService: update listener with current status when registered

This will give an app an opportunity to learn whether an input port is busy
before the user tries to connect and then fails.

Bug: 22825043
Change-Id: Ifede60f166dfe66ea15453044fce06f4a8452b18
Signed-off-by: Phil Burk <philburk@google.com>
(cherry picked from commit b2355940e3e697deeecd1b6511cd5094f9dc553a)
2 files changed