net: snmp: fix 64bit stats on 32bit arches

I accidentally replaced BH disabling by preemption disabling
in SNMP_ADD_STATS64() and SNMP_UPD_PO_STATS64() on 32bit builds.

For 64bit stats on 32bit arch, we really need to disable BH,
since the "struct u64_stats_sync syncp" might be manipulated
both from process and BH contexts.

Fixes: 6aef70a851ac ("net: snmp: kill various STATS_USER() helpers")
Reported-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Tested-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/snmp.h

@@ -166,9 +166,9 @@ struct linux_xfrm_mib {
 
 #define SNMP_ADD_STATS64(mib, field, addend) 				\
 	do {								\
-		preempt_disable();					\
+		local_bh_disable();					\
 		__SNMP_ADD_STATS64(mib, field, addend);			\
-		preempt_enable();					\
+		local_bh_enable();				\
 	} while (0)
 
 #define __SNMP_INC_STATS64(mib, field) SNMP_ADD_STATS64(mib, field, 1)
@@ -184,9 +184,9 @@ struct linux_xfrm_mib {
 	} while (0)
 #define SNMP_UPD_PO_STATS64(mib, basefield, addend)			\
 	do {								\
-		preempt_disable();					\
+		local_bh_disable();					\
 		__SNMP_UPD_PO_STATS64(mib, basefield, addend);		\
-		preempt_enable();					\
+		local_bh_enable();				\
 	} while (0)
 #else
 #define __SNMP_INC_STATS64(mib, field)		__SNMP_INC_STATS(mib, field)