bgp: fix misc evpn prefix match problems caused by using incorrect prefixlen

bgp: fix misc evpn prefix match problems caused by using incorrect prefixlen

The evpn route prefix len was being hardcoded to 224 bits while the
length of a mac-ip addr is actually 288. Because of this many problems were
seen in the evpn-tests. The sample below is from a test that does a vm-move
to verify extended-evpn-mac-mobility - IP1-M1 => IP2->M1. You can see two
local neighs but only one was inserted into the per-vni route table.

root@TORC11:~# net show evpn arp vni 1001 |grep "2001:fee1:0:1::10\|2001:fee1:0:1::11"
2001:fee1:0:1::10       local  active   00:54:6f:7c:74:64
2001:fee1:0:1::11       local  active   00:54:6f:7c:74:64
root@TORC11:~# net show bgp l2vpn evpn route vni 1001 |grep "2001:fee1:0:1::10\|2001:fee1:0:1::11"
*> [2]:[0]:[48]:[00:54:6f:7c:74:64]:[128]:[2001:fee1:0:1::11]
root@TORC11:~#

Similarly other traffic loss problems were seen because of one prefix updating
another prefix's route.

I think the 224-bits came from the packet format definition of type-2 routes.
However the way FRR maintains the key is very different than the format in
the packet so it seems best to just sizeof the addr.

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>