bgpd: Override peer's TTL only if peer-group is configured with TTL

bgpd: Override peer's TTL only if peer-group is configured with TTL

When a peer-group is configured for an already configured eBGP neighbor,
ebgp-multihop command is removed for that peer.

This fix remains configured peer's ebgp-multihop value if peer-group does
not have ebgp-multihop configured.

!
router bgp 100
 neighbor A8 peer-group
 neighbor A9 peer-group
 neighbor A9 ebgp-multihop 12
 neighbor 3.3.3.3 remote-as 123
 neighbor 3.3.3.3 ebgp-multihop 255
 neighbor 4.4.4.4 remote-as 123
 !

spine1-debian-9#
spine1-debian-9# conf
spine1-debian-9(config)# router bgp 100
spine1-debian-9(config-router)# neighbor 3.3.3.3 peer-group A8
spine1-debian-9(config-router)# do sh run

!
router bgp 100
 neighbor A8 peer-group
 neighbor A9 peer-group
 neighbor A9 ebgp-multihop 12
 neighbor 3.3.3.3 remote-as 123
 neighbor 3.3.3.3 peer-group A8
 neighbor 3.3.3.3 ebgp-multihop 255
 neighbor 4.4.4.4 remote-as 123
!

spine1-debian-9(config-router)# neighbor 4.4.4.4 peer-group A9
spine1-debian-9(config-router)# do sh run

!
router bgp 100
 neighbor A8 peer-group
 neighbor A9 peer-group
 neighbor A9 ebgp-multihop 12
 neighbor 3.3.3.3 remote-as 123
 neighbor 3.3.3.3 peer-group A8
 neighbor 3.3.3.3 ebgp-multihop 255
 neighbor 4.4.4.4 remote-as 123
 neighbor 4.4.4.4 peer-group A9
!

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