bfdd: session specific command type checks

bfdd: session specific command type checks

Replace the unclear error message:

```
% Failed to edit configuration.

YANG error(s):
 Schema node not found.
 YANG path: /frr-bfdd:bfdd/bfd/sessions/single-hop[dest-addr='192.168.253.6'][interface=''][vrf='default']/minimum-ttl
```

With:

```
frr(config-bfd-peer)# minimum-ttl 250
% Minimum TTL is only available for multi hop sessions.

! or

frr(config-bfd-peer)# echo
% Echo mode is only available for single hop sessions.
frr(config-bfd-peer)# echo-interval 300
% Echo mode is only available for single hop sessions.
```

Reported-by: Trae Santiago
Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>