apps.mellanox.connectx4: fix mcast counters

The intel_mp driver conflates multicast packets with broadcast
packets, which then needs to be reversed by lib.ipc.shmem.iftable_mib.
We have to do the same here to get conistent MIB counters.  It would
probably be better to properly count the multicast packets in the
Intel driver in the first place.

src/apps/mellanox/connectx4.lua

@@ -1649,19 +1649,27 @@ end
 function HCA:get_port_stats_finish ()
    port_stats.rxbytes = self:output64(0x18 + 0x00) -- includes 4-byte CRC
    local in_ucast_packets = self:output64(0x18 + 0x08)
-   port_stats.rxmcast = self:output64(0x18 + 0x48)
-   port_stats.rxbcast = self:output64(0x18 + 0x50)
+   local in_mcast_packets = self:output64(0x18 + 0x48)
+   local in_bcast_packets = self:output64(0x18 + 0x50)
+   -- This is weird. The intel_mp driver adds broadcast packets to the
+   -- mcast counter, it is unclear why.  Then
+   -- lib.ipc.shmem.iftable_mib reverses it to get the true mcast
+   -- counter back.  So we do the same here.  The proper fix would be
+   -- to fix the Intel driver and remove the anti-hack from
+   -- iftable_mib.
+   port_stats.rxmcast = in_mcast_packets + in_bcast_packets
+   port_stats.rxbcast = in_bcast_packets
    port_stats.rxpackets = in_ucast_packets + port_stats.rxmcast
-      + port_stats.rxbcast
    port_stats.rxdrop = self:output64(0x18 + 0x10)
    port_stats.rxerrors = self:output64(0x18 + 0x18)
 
    port_stats.txbytes = self:output64(0x18 + 0x28)
    local out_ucast_packets = self:output64(0x18 + 0x30)
-   port_stats.txmcast = self:output64(0x18 + 0x58)
-   port_stats.txbcast = self:output64(0x18 + 0x60)
+   local out_mcast_packets = self:output64(0x18 + 0x58)
+   local out_bcast_packets = self:output64(0x18 + 0x60)
+   port_stats.txmcast = out_mcast_packets + out_bcast_packets
+   port_stats.txbcast = out_bcast_packets
    port_stats.txpackets = out_ucast_packets + port_stats.txmcast
-      + port_stats.txbcast
    port_stats.txdrop = self:output64(0x18 + 0x38)
    port_stats.txerrors = self:output64(0x18 + 0x40)
    return port_stats