datapath: No need to zero cb anymore in odp_packet_cmd_execute().

datapath: No need to zero cb anymore in odp_packet_cmd_execute().

Before commit 3f19d399f "datapath: Fix mysterious GRE-over-IPSEC problems,"
'packet' in opd_packet_cmd_execute() was an skb cloned from one created by
Netlink, so its cb member wasn't necessarily zeroed.  But that commit
changed 'packet' to be freshly allocated with __dev_alloc_skb(), which
means that cb is zeroed, so we don't have to do it again.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>