net: erspan: fix erspan config overwrite

net: erspan: fix erspan config overwrite

When an erspan tunnel device receives an erpsan packet with different
tunnel metadata (ex: version, index, hwid, direction), existing code
overwrites the tunnel device's erspan configuration with the received
packet's metadata.  The patch fixes it.

Fixes: 575e64543169 ("gre: add collect_md mode to ERSPAN tunnel")
Fixes: c8f69224f1b5 ("net: erspan: introduce erspan v2 for ip_gre")
Fixes: 8dff97ed081d ("ip6_gre: add ip6 erspan collect_md mode")
Fixes: 2e5542ed6564 ("ip6_gre: add erspan v2 support")
Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>