ENGR00308637 net: fec: fix NULL pointer causing kernel hang

ENGR00308637 net: fec: fix NULL pointer causing kernel hang

Do video mmVector test with below script, kernel will hang after
run about 50 cases.

Script:
mount -o nolock,tcp -t nfs 10.192.224.45:/streams /mnt/streams/
./auto_test.sh -l video_h264_d1.list -AV -n my

Log:
Unable to handle kernel NULL pointer dereference at virtual address 000000a4
pgd = a9c84000
[000000a4] *pgd=a9555831, *pte=00000000, *ppte=00000000
Internal error: Oops: 17 [#1] PREEMPT SMP ARM
Modules linked in: ov5642_camera ov5640_camera evbug
CPU: 0 PID: 16119 Comm: gplay-1.0 Not tainted 3.10.17-internal+g15a353d #1
task: a96183c0 ti: a9de4000 task.ti: a9de4000
PC is at fec_new_rxbdp.isra.28+0x8/0xd8
LR is at fec_enet_rx_napi+0x4b8/0x9a8
pc : [<8039fdf0>]    lr : [<803a0378>]    psr: 60060113
sp : a9de5d30  ip : 00000030  fp : 00000000
r10: a82aa800  r9 : 00000002  r8 : 000001fc
r7 : a82ab000  r6 : 00000000  r5 : ac060fe4  r4 : ac060fe0
r3 : a82ab1fc  r2 : 00000000  r1 : ac060fe4  r0 : a82aa800
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
Control: 10c53c7d  Table: a9c8404a  DAC: 00000015
Process gplay-1.0 (pid: 16119, stack limit = 0xa9de4238)
Stack: (0xa9de5d30 to 0xa9de6000)
5d20:                                     ac060fe0 00000800 00000000 803a0378
5d40: 00000000 a8009240 a8009290 80c6f440 c0802100 a82aa800 a94b1c00 000005ee
5d60: 00000040 00000000 a8ccf480 ac060fe0 a82aacc0 80c95654 80c6edf0 a82aad08
5d80: 00000000 00000001 a82aae14 a82aad98 a9de5dec 8000dca0 a9de4000 a9510240
5da0: a9de5db4 00000001 a82aad98 00000040 0000012c 81537200 0002a165 81537208
5dc0: 80c640c0 8050e878 00000000 80cb5fe5 0002a163 00000001 0000000c 80c64090
5de0: 80c64080 a9de4000 00000003 0000000c 00000100 8002d538 00000096 a800e240
5e00: 80cb5f0e 80c5e7a0 00000000 0000000a 80cf8940 80c640c0 0002a164 a9de4038
5e20: 80c72324 00404000 7eb2b72c 60060193 00000096 00000000 c0802100 a9510240
5e40: a96183c0 00000000 7eb2b72c 8002d6ac a9de4018 8002d948 80c5eef0 8000e94c
5e60: c080210c 80c6a904 a9de5e88 80008558 8008af14 800bfc4c 00060013 ffffffff
5e80: a9de5ebc 8000dc80 00000000 00000000 0000009a 00000000 0000009a 00000000
5ea0: 00080000 a9de5f80 a9510240 a96183c0 00000000 7eb2b72c 00000002 a9de5ed0
5ec0: 8008af14 800bfc4c 00060013 ffffffff 0000009a 00000000 6c41b000 00080000
5ee0: 00000001 a9510240 00000000 00000000 00000000 a96183c0 00000000 00000000
5f00: 0000009a 00000000 00000000 00000000 00080000 00000000 00080000 00000000
5f20: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
5f40: 0002a164 a9510240 6c41b000 a9de5f80 6c41b000 00000001 00080000 800c0290
5f60: 00000002 800d874c 0000009a 00000000 a9510240 6c41b000 00000001 800c08f0
5f80: 0000009a 00000000 c080210c 76eccca8 00000073 76eccca8 00000003 8000e204
5fa0: a9de4000 8000e080 76eccca8 00000073 00000000 6c41b000 00080000 00000010
5fc0: 76eccca8 00000073 76eccca8 00000003 00000000 76eccca8 00000000 7eb2b72c
5fe0: 00000000 7eb2b500 76e59684 76e59694 80060010 00000000 00000000 00000000
[<8039fdf0>] (fec_new_rxbdp.isra.28+0x8/0xd8) from [<a8009240>] (0xa8009240)
Code: eb05b6e9 eafffff1 e92d4070 e1a05001 (e59230a4)
---[ end trace 4362657744775d24 ]---
Kernel panic - not syncing: Fatal exception in interrupt

The issue is caused potential NULL pointer operation in some cases like late
collisions and memory allocate fail by __netdev_alloc_skb_ip_align(). The patch
is to avoid potential NULL pointer operation.

Signed-off-by: Fugang Duan <B38611@freescale.com>