net: pass the struct nlattrs to dump() functions

We'll use this later in the series to get specific information that macvlan
links need.

v2: pass the IFLA_LINKINFO instead of the whole attribute buffer, since
    that's al all we expect the info functions to need, and all we allow
    them to populate on restore

travis-ci: success for series starting with [v10,01/11] net: pass the struct nlattrs to dump() functions
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>