bgpd: snmp MIB bgp4v2 fix indexes in OID

bgpd: snmp MIB bgp4v2 fix indexes in OID

currently snmpwalk give results such :
BGP4V2-MIB::bgp4V2PeerRemoteAddrType.1.ipv6z.10.125.0.2 = INTEGER: ipv4(1)
BGP4V2-MIB::bgp4V2PeerRemoteAddrType.2.dns.253.0.1.37.0.0.0.0.0.0.0.0.0.0.0.3 = INTEGER: ipv6(2)
BGP4V2-MIB::bgp4V2PeerRemoteAddr.1.ipv6z.10.125.0.2 = Hex-STRING: 0A 7D 00 02
BGP4V2-MIB::bgp4V2PeerRemoteAddr.2.dns.253.0.1.37.0.0.0.0.0.0.0.0.0.0.0.3 = Hex-STRING: FD 00 01 25 00 00 00 00 00 00 00 00 00 00 00 03

the expected result is the following

BGP4V2-MIB::bgp4V2PeerRemoteAddrType.1.ipv4.10.125.0.2 = INTEGER: ipv4(1)
BGP4V2-MIB::bgp4V2PeerRemoteAddrType.1.ipv6.253.0.1.37.0.0.0.0.0.0.0.0.0.0.0.3 =
 INTEGER: ipv6(2)
BGP4V2-MIB::bgp4V2PeerRemoteAddr.1.ipv4.10.125.0.2 = Hex-STRING: 0A 7D 00 02
BGP4V2-MIB::bgp4V2PeerRemoteAddr.1.ipv6.253.0.1.37.0.0.0.0.0.0.0.0.0.0.0.3 = Hex
-STRING: FD 00 01 25 00 00 00 00 00 00 00 00 00 00 00 03

in draft-ietf-idr-bgp4-mibv2-11

INDEX for Bgp4V2PeerEntry is define as follows
INDEX {
          bgp4V2PeerInstance,
          bgp4V2PeerRemoteAddrType,
          bgp4V2PeerRemoteAddr
      }

the peer instance is defined as follows
OBJECT bgp4V2PeerInstance
        SYNTAX Unsigned32 (1..4294967295)

more this interpretation is conformant with the snmpwalk implementation
for instance we obtain the following result

swBgp.bgp4V2.bgp4V2Objects.bgp4V2PeerTable.bgp4V2PeerEntry.bgp4V2PeerRemotePort.1.ipv6.253.0.1.37.0.0.0.0.0.0.0.0.0.0.0.3 = Gauge32: 179

swBgp.bgp4V2.bgp4V2Objects.bgp4V2PeerTable.bgp4V2PeerEntry.bgp4V2PeerRemoteAs.1.ipv4.10.125.0.2 = Gauge32: 65200

since currently we are not supporting  multi instance for bgp peer in
SNMP the bgp4V2PeerInstance value is set to 1 coforming to:

"Implementations that do not support multiple routing instances should return 1 for this object."

test is updated accordingly to fix.
currently index for bgp4V2NlriEntry is not coformant to MIB definition

Signed-off-by: Francois Dumontet <francois.dumontet@6wind.com>