bgp: Decode BGP link-bandwidth extended community properly

bgp: Decode BGP link-bandwidth extended community properly

First two bytes are reserved for AS.

Before:
```
	  Extended Community (16), length: 8, Flags [OT]:
	    link-BW (0x4004), Flags [non-transitive]: bandwidth: -308754489798474897524123005616128.000 Mbps
	    0x0000:  4004 fde8 47f4 2400
	  Updated routes:
	    192.168.10.0/23
```

After:
```
	  Extended Community (16), length: 8, Flags [OT]:
	    link-BW (0x4004), Flags [non-transitive]: bandwidth: 1.000 Mbps
	    0x0000:  4004 fde8 47f4 2400
	  Updated routes:
	    192.168.10.0/23
```

Signed-off-by: Donatas Abraitis <[email protected]>