clippy: Fix several clippy issues

In order to enable several clippy lint groups fix several findings.

src/posix/create.rs

@@ -22,17 +22,13 @@ pub struct Create {
 }
 
 fn msgsize_default() -> usize {
-    match fs::read_to_string("/proc/sys/fs/mqueue/msgsize_default") {
-        Ok(m) => m.trim().parse::<usize>().expect("can never fail"),
-        _ => 8192,
-    }
+    fs::read_to_string("/proc/sys/fs/mqueue/msgsize_default")
+        .map_or(8192, |m| m.trim().parse::<usize>().expect("can never fail"))
 }
 
 fn msg_default() -> usize {
-    match fs::read_to_string("/proc/sys/fs/mqueue/msg_default") {
-        Ok(m) => m.trim().parse::<usize>().expect("can never fail"),
-        _ => 10,
-    }
+    fs::read_to_string("/proc/sys/fs/mqueue/msg_default")
+        .map_or(10, |m| m.trim().parse::<usize>().expect("can never fail"))
 }
 
 impl Create {

src/posix/list.rs

@@ -14,12 +14,13 @@ pub struct List {
 
 impl List {
     pub fn run(&self) -> Result<()> {
-        match self.all {
-            false => println!("Name"),
-            true => println!(
+        if self.all {
+            println!(
                 "{0: <10} {1: <10} {2: <12} {3: <26}  {4: <26}",
                 "Name", "Size", "Permissions", "Modified", "Accessed",
-            ),
+            );
+        } else {
+            println!("Name");
         }
 
         for mq in fs::read_dir("/dev/mqueue")? {

src/posix/recv.rs

@@ -36,7 +36,7 @@ fn print_message(priority: u32, length: usize, timestamp: bool, msg: &str) {
         println!("{}", Local::now());
     }
 
-    println!("{}", msg);
+    println!("{msg}");
 }
 
 impl Recv {