bgpd: Respect AFI/SAFI when hard-clearing a peer

bgpd: Respect AFI/SAFI when hard-clearing a peer

The current implementation does not respect the AFI+SAFI combination of
a peer when executing a non-soft (hard) clear. An example would be the
command `clear bgp ipv4 unicast *`, which will clear all BGP peers, even
those that do not have IPv4-Unicast activated.

This commit fixes that behavior by applying the same rules to both soft
and hard clear commands, so that peers without a matching AFI+SAFI
combination will be no longer modified.

Additionally, this commit adds warning messages to all `clear bgp
[<afi>] [<safi>] <target>` commands when no matching peers with the given
AFI+SAFI combination could be found.

Both existing and new warning messages have been extended to also
mention the AFI+SAFI combination that is missing, which is more helpful
to the user than a generic expression 'No peer configured'.

Signed-off-by: Pascal Mathis <mail@pascalmathis.com>