Add the `service.adb.transport` property

adbd reads this property.

Bug: 176210699
Test: boot the system image, check if adb works
Signed-off-by: Roman Kiryanov <rkir@google.com>
Change-Id: I78847022413100331678b68a720aa1f1c8a31130
diff --git a/private/property_contexts b/private/property_contexts
index cea1b6e..6b2b883 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -111,6 +111,7 @@
 
 # adbd protoctl configuration property
 service.adb.tcp.port    u:object_r:adbd_config_prop:s0 exact int
+service.adb.transport   u:object_r:adbd_config_prop:s0 exact string
 
 # Boolean property set by system server upon boot indicating
 # if device is fully owned by organization instead of being