sandbox/seccomp: implement syscall lookup

This uses the Go map and is verified against libseccomp.

Signed-off-by: Ophestra <cat@gensokyo.uk>

sandbox/seccomp/syscall_test.go

@@ -5,12 +5,16 @@ import (
 )
 
 func TestSyscallResolveName(t *testing.T) {
-	for name, want := range syscallNum {
+	for name, want := range Syscalls() {
 		t.Run(name, func(t *testing.T) {
 			if got := syscallResolveName(name); got != want {
 				t.Errorf("syscallResolveName(%q) = %d, want %d",
 					name, got, want)
 			}
+			if got, ok := SyscallResolveName(name); !ok || got != want {
+				t.Errorf("SyscallResolveName(%q) = %d, want %d",
+					name, got, want)
+			}
 		})
 	}
 }