[IPV4]: reset IPCB flags when neccessary

Reset IPSKB_XFRM_TUNNEL_SIZE flags in ipip and ip_gre hard_start_xmit
function before the packet reenters IP. This is neccessary so the
encapsulated packets are checked not to be oversized in xfrm4_output.c
again. Reset all flags in sit when a packet changes its address family.

Also remove some obsolete IPSKB flags.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>