Update userfaultfd to match the version packaged in Fedora which fixes
unrecognized ioctl failures.

--- a/src/firecracker/Cargo.toml
+++ b/src/firecracker/Cargo.toml
@@ -32,7 +32,7 @@
 
 # Dev-Dependencies for uffd examples
 serde = { version = "1.0.193", features = ["derive"] }
-userfaultfd = "0.7.0"
+userfaultfd = "0.8.1"
 
 [build-dependencies]
 bincode = "1.2.1"
--- a/src/vmm/Cargo.toml
+++ b/src/vmm/Cargo.toml
@@ -25,7 +25,7 @@
 timerfd = "1.5.0"
 thiserror = "1.0.32"
 displaydoc = "0.2.4"
-userfaultfd = "0.7.0"
+userfaultfd = "0.8.1"
 versionize = "0.1.10"
 versionize_derive = "0.1.6"
 vhost = { version = "0.9.0", features = ["vhost-user-frontend"] }