fix infoleak in rtnetlink

the stack object “map” has a total size of 32 bytes. Its last 4
bytes are padding generated by compiler. These padding bytes are
not initialized and sent out via “nla_put”

Bug: 28620102

Change-Id: I13da380c6fe8abca49e3cf9f05293c02b44d2e5e
Signed-off-by: kangjie <kangjielu@gmail.com>