bcmwl-kernel-source 6.20.155.1+bdcom-0ubuntu6: bcmwl kernel module failed to build

An error occurred while upgrading from 12.10 to 13.04.

/var/log/dist-upgrade/apt-term.log contains the following lines ...

run-parts: executing /etc/kernel/header_postinst.d/dkms 3.8.0-19-lowlatency /boot/vmlinuz-3.8.0-19-lowlatency
Error! Bad return status for module build on kernel: 3.8.0-19-lowlatency (x86_64)
Consult /var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/make.log for more information.

The contents of /var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/make.log is ...

DKMS make.log for bcmwl-6.20.155.1+bdcom for kernel 3.8.0-19-lowlatency (x86_64)
Sat Apr 27 17:51:02 EST 2013
make: Entering directory `/usr/src/linux-headers-3.8.0-19-lowlatency'
CFG80211 API is prefered for this kernel version
Using CFG80211 API
  LD /var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/built-in.o
  CC [M] /var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/src/shared/linux_osl.o
  CC [M] /var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/src/wl/sys/wl_linux.o
  CC [M] /var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/src/wl/sys/wl_iw.o
  CC [M] /var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/src/wl/sys/wl_cfg80211.o
/var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/src/wl/sys/wl_cfg80211.c:1578:2: warning: initialization from incompatible pointer type [enabled by default]
/var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/src/wl/sys/wl_cfg80211.c:1578:2: warning: (near initialization for ‘wl_cfg80211_ops.set_tx_power’
) [enabled by default]
/var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/src/wl/sys/wl_cfg80211.c:1579:2: warning: initialization from incompatible pointer type [enabled by default]
/var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/src/wl/sys/wl_cfg80211.c:1579:2: warning: (near initialization for ‘wl_cfg80211_ops.get_tx_power’) [enabled by default]
  LD [M] /var/lib/dkms/bcmwl/6.20.155.1+bdcom/build/wl.o
  Building modules, stage 2.
CFG80211 API is prefered for this kernel version
Using CFG80211 API
  MODPOST 1 modules
FATAL: modpost: GPL-incompatible module wl.ko uses GPL-only symbol '__rcu_read_unlock'
make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2
make: Leaving directory `/usr/src/linux-headers-3.8.0-19-lowlatency'

ProblemType: Package
DistroRelease: Ubuntu 13.04
Package: bcmwl-kernel-source 6.20.155.1+bdcom-0ubuntu6
ProcVersionSignature: Ubuntu 3.8.0-19.29-generic 3.8.8
Uname: Linux 3.8.0-19-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
DKMSKernelVersion: 3.8.0-19-lowlatency
Date: Sat Apr 27 17:51:21 2013
InstallationDate: Installed on 2010-05-19 (1074 days ago)
InstallationMedia: Kubuntu 10.04 LTS "Lucid Lynx" - Release amd64 (20100427)
MarkForUpload: True
PackageVersion: 6.20.155.1+bdcom-0ubuntu6
SourcePackage: bcmwl
Title: bcmwl-kernel-source 6.20.155.1+bdcom-0ubuntu6: bcmwl kernel module failed to build
UpgradeStatus: Upgraded to raring on 2013-04-27 (0 days ago)