bonding: refine IFF_XMIT_DST_RELEASE capability

bonding: refine IFF_XMIT_DST_RELEASE capability

Some workloads greatly benefit of IFF_XMIT_DST_RELEASE capability
on output net device, avoiding dirtying dst refcount.

bonding currently disables IFF_XMIT_DST_RELEASE unconditionally.

If all slaves have the IFF_XMIT_DST_RELEASE bit set, then
bonding master can also have it in its priv_flags

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Jay Vosburgh <[email protected]>
Cc: Andy Gospodarek <[email protected]>
Cc: Tom Herbert <[email protected]>
Signed-off-by: David S. Miller <[email protected]>