net: fix endian check warning in etherdevice.h

commit fbaff3ef upstream.

Sparse builds have been warning for a really long time now
that etherdevice.h has a conversion that is unsafe.

  include/linux/etherdevice.h:79:32: warning: restricted __be16 degrades to integer

This code change fixes the issue and generates the exact
same assembly before/after (checked on x86_64)

Fixes: 2c722fe1 (etherdevice: Optimize a few is_<foo>_ether_addr functions)
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
CC: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

include/linux/etherdevice.h

@@ -72,7 +72,7 @@ static inline bool is_link_local_ether_addr(const u8 *addr)
 
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
 	return (((*(const u32 *)addr) ^ (*(const u32 *)b)) |
-		((a[2] ^ b[2]) & m)) == 0;
+		(__force int)((a[2] ^ b[2]) & m)) == 0;
 #else
 	return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | ((a[2] ^ b[2]) & m)) == 0;
 #endif