net: checksum: drop the linux/uaccess.h include

net/checksum.h pulls in linux/uaccess.h which is large.

In the x86 header the include seems to not be needed at all.
ARM on the other hand does not include uaccess.h, even tho
it calls access_ok().

In the generic implementation guard the include of linux/uaccess.h
with the same condition as the code that needs it.

With this change pre-processed net/checksum.h shrinks on x86
from 30616 lines to just 1193.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/arm/include/asm/checksum.h

@@ -11,6 +11,7 @@
 #define __ASM_ARM_CHECKSUM_H
 
 #include <linux/in6.h>
+#include <linux/uaccess.h>
 
 /*
  * computes the checksum of a memory block at buff, length len,

arch/x86/include/asm/checksum_64.h

@@ -9,7 +9,6 @@
  */
 
 #include <linux/compiler.h>
-#include <linux/uaccess.h>
 #include <asm/byteorder.h>
 
 /**

include/net/checksum.h

@@ -18,8 +18,10 @@
 #include <linux/errno.h>
 #include <asm/types.h>
 #include <asm/byteorder.h>
-#include <linux/uaccess.h>
 #include <asm/checksum.h>
+#if !defined(_HAVE_ARCH_COPY_AND_CSUM_FROM_USER) || !defined(HAVE_CSUM_COPY_USER)
+#include <linux/uaccess.h>
+#endif
 
 #ifndef _HAVE_ARCH_COPY_AND_CSUM_FROM_USER
 static __always_inline