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"] }