lttng-modules-dkms fails to build on updated Utopic kernel

Rationale:

lttng-modules-dkms won't build on updated Utopic kernels.

Testcase:

Install lttng-modules-dkms on Utopic

Regression potential:

None, current package won't build modules or install.

Error during build:
DKMS make.log for lttng-modules-2.5.0 for kernel 3.16.0-28-generic (x86_64)
Fri Dec 12 16:39:01 EST 2014
make: Entering directory '/usr/src/linux-headers-3.16.0-28-generic'
  CC [M] /var/lib/dkms/lttng-modules/2.5.0/build/lttng-ring-buffer-client-discard.o
  CC [M] /var/lib/dkms/lttng-modules/2.5.0/build/lttng-ring-buffer-client-overwrite.o
  CC [M] /var/lib/dkms/lttng-modules/2.5.0/build/lttng-ring-buffer-metadata-client.o
  CC [M] /var/lib/dkms/lttng-modules/2.5.0/build/lttng-ring-buffer-client-mmap-discard.o
  CC [M] /var/lib/dkms/lttng-modules/2.5.0/build/lttng-ring-buffer-client-mmap-overwrite.o
  CC [M] /var/lib/dkms/lttng-modules/2.5.0/build/lttng-ring-buffer-metadata-mmap-client.o
  CC [M] /var/lib/dkms/lttng-modules/2.5.0/build/lttng-statedump-impl.o
/var/lib/dkms/lttng-modules/2.5.0/build/lttng-statedump-impl.c: In function ‘lttng_statedump_process_ns’:
/var/lib/dkms/lttng-modules/2.5.0/build/lttng-statedump-impl.c:393:2: error: implicit declaration of function ‘task_nsproxy’ [-Werror=implicit-function-declaration]
  proxy = task_nsproxy(p);
  ^
/var/lib/dkms/lttng-modules/2.5.0/build/lttng-statedump-impl.c:393:8: warning: assignment makes pointer from integer without a cast
  proxy = task_nsproxy(p);
        ^
cc1: some warnings being treated as errors
scripts/Makefile.build:257: recipe for target '/var/lib/dkms/lttng-modules/2.5.0/build/lttng-statedump-impl.o' failed
make[1]: *** [/var/lib/dkms/lttng-modules/2.5.0/build/lttng-statedump-impl.o] Error 1
Makefile:1345: recipe for target '_module_/var/lib/dkms/lttng-modules/2.5.0/build' failed
make: *** [_module_/var/lib/dkms/lttng-modules/2.5.0/build] Error 2
make: Leaving directory '/usr/src/linux-headers-3.16.0-28-generic'