bonding: use local function pointer of bond->recv_probe in bond_handle_frame

The bond->recv_probe is called in bond_handle_frame() when
a packet is received, but bond_close() sets it to NULL. So,
a panic occurs when both functions work in parallel.

Why this happen:
After null pointer check of bond->recv_probe, an sk_buff is
duplicated and bond->recv_probe is called in bond_handle_frame.
So, a panic occurs when bond_close() is called between the
check and call of bond->recv_probe.

Patch:
This patch uses a local function pointer of bond->recv_probe
in bond_handle_frame(). So, it can avoid the null pointer
dereference.

Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
Cc: Jay Vosburgh <fubar@us.ibm.com>
Cc: Andy Gospodarek <andy@greyhouse.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>