Support src_mac, dst_mac and vlan id in flower filters

[shuowang-123]

See title, so users are able to filter flower rules based on src/dst mac address. I ran the test on an Oracle Linux 8 virtual machine and it passed:

[] go test -run "TestFilterFlowerAddDel"
PASS
ok github.com/vishvananda/netlink 0.017s

I also ran the test (without cleanup) on the same machine, was able to see the flower rule was created correctly, as reported by "tc":

[] ip netns exec netns1 tc filter show dev foo ingress
filter parent ffff: protocol all pref 1 flower chain 0
filter parent ffff: protocol all pref 1 flower chain 0 handle 0x1
dst_mac 2c:54:91:88:c9:e5
src_mac 2c:54:91:88:c9:e3
eth_type ipv4
dst_ip 1.0.0.1/24
src_ip 2.0.0.1/24
enc_dst_ip 3.0.0.1/24
enc_src_ip 4.0.0.1/24
enc_key_id 1234
enc_dst_port 8472
not_in_hw
action order 1: mirred (Egress Redirect to device bar) stolen
index 1 ref 1 bind 1

[shuowang-123]

This should address second request from #589

[aboch]

@shuowang-123