enic: fix initialization error with clang

enic: fix initialization error with clang

This patch fixes the following compiler error raised by clang 3.3
on FreeBSD 10:

  CC enic_clsf.o
lib/librte_pmd_enic/enic_clsf.c:99:25: fatal error: missing field 'u' initializer [-Wmissing-field-initializers]
        struct filter fltr = {0};

It fixes it by changing the initializer to set a named field to zero,
thereby automatically setting the rest of the unnamed fields also to
zero.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>