net: avoid reloads in SNMP_UPD_PO_STATS

Avoid two instructions to reload dev->nd_net->mib.ip_statistics pointer,
unsing a temp variable, in ip_rcv(), ip_output() paths for example.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/snmp.h

@@ -154,13 +154,15 @@ struct linux_xfrm_mib {
  */
 #define SNMP_UPD_PO_STATS(mib, basefield, addend)	\
 	do { \
-		this_cpu_inc(mib[0]->mibs[basefield##PKTS]);		\
-		this_cpu_add(mib[0]->mibs[basefield##OCTETS], addend);	\
+		__typeof__(*mib[0]->mibs) *ptr = mib[0]->mibs;	\
+		this_cpu_inc(ptr[basefield##PKTS]);		\
+		this_cpu_add(ptr[basefield##OCTETS], addend);	\
 	} while (0)
 #define SNMP_UPD_PO_STATS_BH(mib, basefield, addend)	\
 	do { \
-		__this_cpu_inc(mib[0]->mibs[basefield##PKTS]);		\
-		__this_cpu_add(mib[0]->mibs[basefield##OCTETS], addend);	\
+		__typeof__(*mib[0]->mibs) *ptr = mib[0]->mibs;	\
+		__this_cpu_inc(ptr[basefield##PKTS]);		\
+		__this_cpu_add(ptr[basefield##OCTETS], addend);	\
 	} while (0)