dp-packet: Fix use of uninitialised value at emc_lookup.

Valgrind reports "Conditional jump or move depends on uninitialised value"
and "Use of uninitialised value" at case 2016 ovn -- 3 HVs, 1 LS, 3
lports/HV.  It is caused by 1) assigning an uninitialized value to 'key->hash'
at emc_processing(). Due to uninit rss_hash_valid, dp_packet_rss_valid() might
return true and undefined hash value is returned, and 2) at emc_lookup, the
'current_entry->key.hash' could be uninitialized due to dp_packet_clone().
The patch fixes the two and as a result, a couple of calls to
dp_packet_rss_invalidate() become redundant and thus are removed.

Call stacks:
- Connditional jump or move depends on uninitialised value(s)
    dpif_netdev_packet_get_rss_hash (dpif-netdev.c:3334)
    emc_processing (dpif-netdev.c:3455)
    dp_netdev_input__ (dpif-netdev.c:3639)
and,
- Use of uninitialised value of size 8
    emc_lookup (dpif-netdev.c:1785)
    emc_processing (dpif-netdev.c:3457)
    dp_netdev_input__ (dpif-netdev.c:3639)

Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>

lib/netdev-linux.c

@@ -1116,7 +1116,6 @@ netdev_linux_rxq_recv(struct netdev_rxq *rxq_, struct dp_packet **packets,
         dp_packet_delete(buffer);
     } else {
         dp_packet_pad(buffer);
-        dp_packet_rss_invalidate(buffer);
         packets[0] = buffer;
         *c = 1;
     }