r8152: remove some bit operations

Remove DELL_TB_RX_AGG_BUG and LENOVO_MACPASSTHRU flags of rtl8152_flags.
They are only set when initializing and wouldn't be change. It is enough
to record them with variables.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>