vmxnet3: avoid calling pskb_may_pull with interrupts disabled

vmxnet3 has a function vmxnet3_parse_and_copy_hdr which, among other operations,
uses pskb_may_pull to linearize the header portion of an skb.  That operation
eventually uses local_bh_disable/enable to ensure that it doesn't race with the
drivers bottom half handler.  Unfortunately, vmxnet3 preforms this
parse_and_copy operation with a spinlock held and interrupts disabled.  This
causes us to run afoul of the WARN_ON_ONCE(irqs_disabled()) warning in
local_bh_enable, resulting in this:

WARNING: at kernel/softirq.c:159 local_bh_enable+0x59/0x90() (Not tainted)
Hardware name: VMware Virtual Platform
Modules linked in: ipv6 ppdev parport_pc parport microcode e1000 vmware_balloon
vmxnet3 i2c_piix4 sg ext4 jbd2 mbcache sd_mod crc_t10dif sr_mod cdrom mptspi
mptscsih mptbase scsi_transport_spi pata_acpi ata_generic ata_piix vmwgfx ttm
drm_kms_helper drm i2c_core dm_mirror dm_region_hash dm_log dm_mod [last
unloaded: mperf]
Pid: 6229, comm: sshd Not tainted 2.6.32-616.el6.i686 #1
Call Trace:
 [<c04624d9>] ? warn_slowpath_common+0x89/0xe0
 [<c0469e99>] ? local_bh_enable+0x59/0x90
 [<c046254b>] ? warn_slowpath_null+0x1b/0x20
 [<c0469e99>] ? local_bh_enable+0x59/0x90
 [<c07bb936>] ? skb_copy_bits+0x126/0x210
 [<f8d1d9fe>] ? ext4_ext_find_extent+0x24e/0x2d0 [ext4]
 [<c07bc49e>] ? __pskb_pull_tail+0x6e/0x2b0
 [<f95a6164>] ? vmxnet3_xmit_frame+0xba4/0xef0 [vmxnet3]
 [<c05d15a6>] ? selinux_ip_postroute+0x56/0x320
 [<c0615988>] ? cfq_add_rq_rb+0x98/0x110
 [<c0852df8>] ? packet_rcv+0x48/0x350
 [<c07c5839>] ? dev_queue_xmit_nit+0xc9/0x140
...

Fix it by splitting vmxnet3_parse_and_copy_hdr into two functions:

vmxnet3_parse_hdr, which sets up the internal/on stack ctx datastructure, and
pulls the skb (both of which can be done without holding the spinlock with irqs
disabled

and

vmxnet3_copy_header, which just copies the skb to the tx ring under the lock
safely.

tested and shown to correct the described problem.  Applies cleanly to the head
of the net tree

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Shrikrishna Khare <skhare@vmware.com>
CC: "VMware, Inc." <pv-drivers@vmware.com>
CC: "David S. Miller" <davem@davemloft.net>
Acked-by: Shrikrishna Khare <skhare@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>