bgpd: Use IEEE-754 Floating Point for storing extcommunity bandwidth

bgpd: Use IEEE-754 Floating Point for storing extcommunity bandwidth

https://datatracker.ietf.org/doc/html/draft-ietf-idr-link-bandwidth-07 says:

The bandwidth of the link is expressed as 4
   octets in IEEE floating point format, units being bytes (not bits!)
   per second.  It is carried in the Local Administrator subfield of the
   Value Field.

Before:

```
	  Extended Community (16), length: 8, Flags [OT]:
	    unknown extd community typecode (0x0004), Flags [none]
	      0x0000:  0004 fdeb 0001 e848
	    0x0000:  0004 fdeb 0001 e848
	  Updated routes:
	    172.16.16.1/32
```

0001 e848 - means 125000 (1Mbps), which is encoded incorrect.

After:

```
	  Extended Community (16), length: 8, Flags [OT]:
	    unknown extd community typecode (0x0004), Flags [none]
	      0x0000:  0004 fdeb 47f4 2400
	    0x0000:  0004 fdeb 47f4 2400
	  Updated routes:
	    172.16.16.1/32
```

47f4 2400 - means the same, but in floating point format.

Signed-off-by: Donatas Abraitis <donatas.abraitis@gmail.com>