net/filter-mirror.c: Rename filter_mirror_send() and fix codestyle

Because filter_mirror_receive_iov() and filter_redirector_receive_iov()
both use the filter_mirror_send() to send packet, so I change
filter_mirror_send() to filter_send() that looks more common.
And fix some codestyle.

Signed-off-by: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>