bgpd: Add `set as-path replace <any|ASN>` cmd for route-maps

```
route-map tstas permit 10
 set as-path replace 1
exit
```

Before:

```
donatas-laptop(config-router-af)# do show ip bgp 10.10.10.10/32
BGP routing table entry for 10.10.10.10/32, version 13
Paths: (1 available, best #1, table default)
  Advertised to non peer-group peers:
  192.168.10.65
  65000 1 2 3 123
    192.168.10.65 from 192.168.10.65 (10.10.10.11)
      Origin IGP, metric 0, valid, external, best (First path received)
      Last update: Mon Apr 25 10:39:50 2022
```

After:

```
donatas-laptop(config-router-af)# do show ip bgp 10.10.10.10/32
BGP routing table entry for 10.10.10.10/32, version 15
Paths: (1 available, best #1, table default)
  Advertised to non peer-group peers:
  192.168.10.65
  65000 65010 2 3 123
    192.168.10.65 from 192.168.10.65 (10.10.10.11)
      Origin IGP, metric 0, valid, external, best (First path received)
      Last update: Mon Apr 25 10:40:16 2022
```

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

1 files changed, 22 insertions, 0 deletions

diff --git a/bgpd/bgp_aspath.c b/bgpd/bgp_aspath.c
index fd644ebf0..880e15fad 100644
--- a/bgpd/bgp_aspath.c
+++ b/bgpd/bgp_aspath.c
@@ -1258,6 +1258,28 @@ struct aspath *aspath_replace_specific_asn(struct aspath *aspath,
 	return new;
 }
 
+/* Replace all ASNs with our own ASN */
+struct aspath *aspath_replace_all_asn(struct aspath *aspath, as_t our_asn)
+{
+	struct aspath *new;
+	struct assegment *seg;
+
+	new = aspath_dup(aspath);
+	seg = new->segments;
+
+	while (seg) {
+		int i;
+
+		for (i = 0; i < seg->length; i++)
+			seg->as[i] = our_asn;
+
+		seg = seg->next;
+	}
+
+	aspath_str_update(new, false);
+	return new;
+}
+
 /* Replace all private ASNs with our own ASN */
 struct aspath *aspath_replace_private_asns(struct aspath *aspath, as_t asn,
 					   as_t peer_asn)