face: silence silly warning thrown by clang.

Clang 3.3 complains about a "missing field initializer" for struct ifreq.
However, according to the standard, if there are fewer initializers in a
brace-enclosed list than there are elements or members of an aggregate,
the remainder of the aggregate shall be initialized implicitly as if they
were declared static, i.e. with zero or default-constructed value.

Therefore using "= {0}" is correct (and common practice in C). Emitting
a warning doesn't make sense. As a matter of fact recent GCC releases
disabled it.

Luckily this is C++ and we can simply use the "empty braces" initializer
(which wouldn't be valid C99 syntax) to silence the compiler.

Change-Id: Ibee8d17cc9b5d0eaa5270c52f3596b7994b5e911