net_gen: replace net_gen with libc

The libc crate provides all functionality provided by the net_gen crate.
Removing the net_gen crate reduces the maintenance burden.

The switch to libc required some fixes, most notably the switch from a
`Vec<u8>` to a `CString` for the `net_util::Tap.if_name` field.

On-behalf-of: SAP julian.schindel@sap.com
Signed-off-by: Julian Schindel <julian.schindel@cyberus-technology.de>

fuzz/Cargo.lock

@@ -801,13 +801,6 @@ dependencies = [
  "zerocopy",
 ]
 
-[[package]]
-name = "net_gen"
-version = "0.1.0"
-dependencies = [
- "vmm-sys-util",
-]
-
 [[package]]
 name = "net_util"
 version = "0.1.0"
@@ -816,7 +809,6 @@ dependencies = [
  "getrandom 0.4.2",
  "libc",
  "log",
- "net_gen",
  "rate_limiter",
  "serde",
  "thiserror",
@@ -1235,7 +1227,6 @@ dependencies = [
  "anyhow",
  "libc",
  "log",
- "net_gen",
  "thiserror",
  "vmm-sys-util",
 ]