1. Priority field decode.
The 802.1q tag field of a frame is separated from its frame body in
a ERSPAN packet.
Current packet-cisco-erspan.c decodes only the vlan id field of the
802.1q tag.
This patch can also decode the priority field of the 802.1q tag.
2. Direction of a captured frame decode.
A ERSPAN packet includes the additional information of the direction
a captured frame as below.
If a caputred frame comes from outside to a switch port, this means an
'Incoming' frame. If a caputred frame goes out of a switch port,
this is an 'Outgoing' frame.
Added an extra unknown value for the bit between direction and spanid.
svn path=/trunk/; revision=22649
Guy Harris