Upgrade rust/crates/vsock to 0.2.4

Test: make
Change-Id: I2b8243e2b6b10866c9778ff4d1d3050faee2f62a
diff --git a/Android.bp b/Android.bp
index 36b9fb8..5e4e836 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,4 +1,5 @@
 // This file is generated by cargo2android.py --run --device --dependencies.
+// Do not modify this file as changes will be overridden on upgrade.
 
 package {
     default_applicable_licenses: ["external_rust_crates_vsock_license"],
@@ -32,5 +33,5 @@
 // dependent_library ["feature_list"]
 //   bitflags-1.2.1 "default"
 //   cfg-if-1.0.0
-//   libc-0.2.86 "default,extra_traits,std"
+//   libc-0.2.97 "default,extra_traits,std"
 //   nix-0.19.1