staging: et131x: Remove struct tcb->flags

'struct tcb' member 'flags' was only used to collect tx stats, now
we are no longer collecting those particular stats, we no longer
need tcb->flags or the code used to peek into the skb to set it's
value.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>