bgpd: Initialize attr->local_pref to the configured default value

bgpd: Initialize attr->local_pref to the configured default value

When we use network/redistribute local_preference is configured inproperly
when using route-maps something like:

```
network 100.100.100.100/32 route-map rm1
network 100.100.100.200/32 route-map rm2

route-map rm1 permit 10
 set local-preference +10
route-map rm2 permit 10
 set local-preference -10
```

Before:
```
root@spine1-debian-11:~# vtysh -c 'show bgp ipv4 unicast 100.100.100.100/32 json' | jq '.paths[].locPrf'
10
root@spine1-debian-11:~# vtysh -c 'show bgp ipv4 unicast 100.100.100.200/32 json' | jq '.paths[].locPrf'
0
```

After:
```
root@spine1-debian-11:~# vtysh -c 'show bgp ipv4 unicast 100.100.100.100/32 json' | jq '.paths[].locPrf'
110
root@spine1-debian-11:~# vtysh -c 'show bgp ipv4 unicast 100.100.100.200/32 json' | jq '.paths[].locPrf'
90
```

Set local-preference as the default value configured per BGP instance, but
do not set LOCAL_PREF flag by default.

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>