net/e1000: correct VLAN tag byte order for i35x LB packets

net/e1000: correct VLAN tag byte order for i35x LB packets

When copying VLAN tags from the RX descriptor to the vlan_tci field
in the mbuf header,  igb_rxtx.c:eth_igb_recv_pkts() and
eth_igb_recv_scattered_pkts() both assume that the VLAN tag is always
little endian.  While i350, i354 and /i350vf VLAN non-loopback
packets are stored little endian, VLAN tags in loopback packets (LB)
for those devices are big endian.

For i350, i354 and i350vf VLAN loopback packets, swap the tag when
copying from the RX descriptor to the mbuf header.  This will ensure
that the mbuf vlan_tci is always little endian.

Signed-off-by: Roger Melton <rmelton@cisco.com>
Acked-by: Wenzhuo Lu <wenzhuo.lu@intel.com>