examples: fix vlan_learning example
examples: fix vlan_learning example

BPF_HASH declaration fixed.

brendangregg/bcc,brendangregg/bcc,brendangregg/bcc,tuxology/bcc,mcaleavya/bcc,mcaleavya/bcc,iovisor/bcc,iovisor/bcc,tuxology/bcc,brendangregg/bcc,mcaleavya/bcc,mcaleavya/bcc,iovisor/bcc,tuxology/bcc,iovisor/bcc,iovisor/bcc,tuxology/bcc,tuxology/bcc,brendangregg/bcc,mcaleavya/bcc