[ewg] Fix for panic in ib_core

[Arjun Vynipadath]

Hey Vlad,

While testing RHEL7.5 backports, panic was observed. This patch from 
https://github.com/arjunvynipadath/compat-rdma/commits/master
fixes it. Please pull this into OFED:
---------------------------------------------
commit 1024c8ba9bc32b3d56ae1595fb28b329b309c68f
Author: Arjun Vynipadath <arjun at chelsio.com>
Date:   Wed Jul 11 11:02:18 2018 +0530

    ib_core: Fix NULL pointer dereference while registering netdevice

    Fixes the below NULL pointer dereference seen when loading ib_core

    BUG: unable to handle kernel paging request at 0000000000007130
    IP: [<ffffffffc0bca438>] netdevice_event+0x48/0x380 [ib_core]
    PGD 800000009b5c4067 PUD d2f03067 PMD 0
    Oops: 0000 [#1] SMP
    Modules linked in: ib_core(OE+) macsec vsock_diag vsock sctp_diag sctp tcp_diag udp_diag inet_diag unix_diag af_packet_diag netlink_diag binfmt_misc xt_CH
     syscopyarea sysfillrect sysimgblt fb_sys_fops ttm ata_generic pata_acpi drm ata_piix libata crc32c_intel e1000e mptsas serio_raw scsi_transport_sas mptsc
    CPU: 2 PID: 7402 Comm: insmod Kdump: loaded Tainted: G          IOE  ------------   3.10.0-862.el7.x86_64 #1
    Hardware name: Supermicro X8ST3/X8ST3, BIOS 2.0        07/29/10
    task: ffff8a598b5d0fd0 ti: ffff8a59cedc0000 task.ti: ffff8a59cedc0000
    RIP: 0010:[<ffffffffc0bca438>]  [<ffffffffc0bca438>] netdevice_event+0x48/0x380 [ib_core]
    RSP: 0018:ffff8a59cedc3c18  EFLAGS: 00010246
    RAX: 0000000000000045 RBX: 0000000000006f6c RCX: 0000000000000000
    RDX: 0000000000000000 RSI: ffff8a5a1f293938 RDI: ffff8a5a1f293938
    RBP: ffff8a59cedc3c98 R08: 000000000000000a R09: 0000000000000000
    R10: 0000000000000494 R11: ffff8a59cedc3916 R12: ffff8a5a1cfef000
    R13: 0000000000000005 R14: 0000000000000000 R15: ffffffffa22fc9c8
    FS:  00007fe58c4f2740(0000) GS:ffff8a5a1f280000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    CR2: 0000000000007130 CR3: 00000000d04ba000 CR4: 00000000000007e0
    Call Trace:
     [<ffffffffc0bca3f0>] ? is_eth_port_inactive_slave+0x40/0x40 [ib_core]
     [<ffffffffa1be5cd8>] __register_netdevice_notifier+0xa8/0x200
     [<ffffffffc0bf9000>] ? 0xffffffffc0bf8fff
     [<ffffffffa1be5e43>] register_netdevice_notifier+0x13/0x20
     [<ffffffffc0bf9261>] roce_gid_mgmt_init+0x51/0x5c [ib_core]
     [<ffffffffc0bf9192>] ib_cache_setup+0x9/0xb [ib_core]
     [<ffffffffc0bf913f>] __init_backport+0x13f/0x189 [ib_core]
     [<ffffffffa160210a>] do_one_initcall+0xba/0x240
     [<ffffffffa170f5ac>] load_module+0x272c/0x2bc0
     [<ffffffffa19767a0>] ? ddebug_proc_write+0xf0/0xf0
     [<ffffffffa170b1e3>] ? copy_module_from_fd.isra.43+0x53/0x150
     [<ffffffffa170fbf6>] SyS_finit_module+0xa6/0xd0
     [<ffffffffa1d1f7d5>] system_call_fastpath+0x1c/0x21
     [<ffffffffa1d1f721>] ? system_call_after_swapgs+0xae/0x146
    Code: 89 e6 53 48 83 ec 68 48 8b 1a 65 48 8b 04 25 28 00 00 00 48 89 45 e0 31 c0 48 89 da f3 48 ab 48 c7 c7 70 37 be c0 e8 69 d7 13 e1 <66> 83 bb c4 01 00
    RIP  [<ffffffffc0bca438>] netdevice_event+0x48/0x380 [ib_core]
     RSP <ffff8a59cedc3c18>
    CR2: 0000000000007130

    Signed-off-by: Arjun Vynipadath <arjun at chelsio.com>

-----------------------------------------------------------

Thanks,
Arjun.