lxc_user_nic was segfaulting:
lxc-user-nic[9761]: segfault at 29 ip 00007f3fb2346872 sp 00007ffdd17b2dd0 error 4 in libc-2.21.so[7f3fb22c2000+1c0000

This patch fixes it.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>