linux(4): Cleanup sys/sysent.h from linux_util

Include sys/sysent.h directly where it needed. The linux_util.h included
in a most source files of the Linuxulator, avoid collecting a rarely used
includes here.

MFC after:		2 weeks

sys/compat/linux/linux_futex.c

@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/priv.h>
 #include <sys/proc.h>
 #include <sys/sched.h>
+#include <sys/sysent.h>
 #include <sys/umtxvar.h>
 
 #ifdef COMPAT_LINUX32

sys/compat/linux/linux_ipc.c

@@ -39,6 +39,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/sem.h>
 #include <sys/shm.h>
 #include <sys/stat.h>
+#include <sys/sysent.h>
 
 #ifdef COMPAT_LINUX32
 #include <machine/../linux32/linux.h>

sys/compat/linux/linux_misc.c

@@ -64,6 +64,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/stat.h>
 #include <sys/syscallsubr.h>
 #include <sys/sysctl.h>
+#include <sys/sysent.h>
 #include <sys/sysproto.h>
 #include <sys/systm.h>
 #include <sys/time.h>

sys/compat/linux/linux_util.h

@@ -36,7 +36,6 @@
 #ifndef	_LINUX_UTIL_H_
 #define	_LINUX_UTIL_H_
 
-#include <sys/sysent.h>
 #include <sys/uio.h>
 
 MALLOC_DECLARE(M_LINUX);