rust/bt-gatt: Add ResolvableSetIdentifier to AdvertisingDatum

Add the `ResolvableSetIdentifier` variant to support parsing the 6-byte
RSI AD type. This enables the CSIP Set Coordinator to identify set
members during scanning without connecting.

Test: cargo check
Change-Id: I0fd2c01e620fa86907d9b942311545b36dce65b2
Reviewed-on: https://bluetooth-review.googlesource.com/c/bluetooth/+/3260

rust/bt-gatt/src/central.rs

diff --git a/rust/bt-gatt/src/central.rs b/rust/bt-gatt/src/central.rs
index af55cd0..0bf0802 100644
--- a/rust/bt-gatt/src/central.rs
+++ b/rust/bt-gatt/src/central.rs
@@ -21,6 +21,7 @@
     TxPowerLevel(i8),
     Uri(String),
     BroadcastName(String),
+    ResolvableSetIdentifier([u8; 6]),
 }
 
 /// Matches a single advertised attribute or condition from a Bluetooth Low