sim: Add swap using offset to tests

Enables testing this new mode

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/sim/Cargo.toml b/sim/Cargo.toml
index 7cef823..6d2262d 100644
--- a/sim/Cargo.toml
+++ b/sim/Cargo.toml
@@ -15,6 +15,7 @@
 sig-p384 = ["mcuboot-sys/sig-p384"]
 sig-ed25519 = ["mcuboot-sys/sig-ed25519"]
 overwrite-only = ["mcuboot-sys/overwrite-only"]
+swap-offset = ["mcuboot-sys/swap-offset"]
 swap-move = ["mcuboot-sys/swap-move"]
 validate-primary-slot = ["mcuboot-sys/validate-primary-slot"]
 enc-rsa = ["mcuboot-sys/enc-rsa"]