Block original umount syscall in default seccomp filter

The original umount syscall without flags argument needs to
be blocked too.

Signed-off-by: Justin Cormack <justin.cormack@unikernel.com>

daemon/execdriver/native/seccomp_default.go

@@ -298,6 +298,12 @@ var defaultSeccompProfile = &configs.Seccomp{
 			Action: configs.Errno,
 			Args:   []*configs.Arg{},
 		},
+		{
+			// Deny umount
+			Name:   "umount",
+			Action: configs.Errno,
+			Args:   []*configs.Arg{},
+		},
 		{
 			// Deny umount
 			Name:   "umount2",