Enables packetfilter ext in NEC plugin based on its driver config

packet filter extension in NEC plugin should be determined based on
a return value of filter_supported method in the backend driver.
Previously filter_supported was not called actually and packetfilter
extension was always enabled.

Fixes bug #1133100

Change-Id: I1334c7695e64bc942c0ecce2bd85e5a92e75b388
Merge "Enables packetfilter ext in NEC plugin based on its driver config"