Disable BFD multihop support in Frontend

[zolug]

Description

Adjust BIRD config to disable BFD multihop, thus do not create a listener socket for the multihop port (4784).

https://bird.network.cz/?get_doc&v=20&f=bird-6.html#ss6.3

accept [ipv4|ipv6] [direct|multihop]
A BFD protocol instance accepts (by default) all BFD session requests (with regard to VRF restrictions, see above). This option controls whether IPv4 / IPv6 and direct / multihop session requests are accepted (and which listening sockets are opened). It can be used, for example, to configure separate BFD protocol instances for IPv4 and for IPv6 sessions.

Before:

root@stateless-lb-frontend-attr-a1-5b5757c6c4-jdm4r:/home/ezollug/work/kind# ss -lpu
State            Recv-Q           Send-Q                              Local Address:Port                      Peer Address:Port           Process                                       
UNCONN           0                0                          169.254.100.1%eth0.100:50388                          0.0.0.0:*               users:(("bird",pid=1795212,fd=19))           
UNCONN           0                0                                         0.0.0.0:3784                           0.0.0.0:*               users:(("bird",pid=1795212,fd=12))           
UNCONN           0                0                                         0.0.0.0:4784                           0.0.0.0:*               users:(("bird",pid=1795212,fd=13))           
UNCONN           0                0                           [100:100::1]%eth0.100:57934                             [::]:*               users:(("bird",pid=1795212,fd=16))           
UNCONN           0                0                                            [::]:3784                              [::]:*               users:(("bird",pid=1795212,fd=14))           
UNCONN           0                0                                            [::]:4784                              [::]:*               users:(("bird",pid=1795212,fd=15)) 

After:

root@stateless-lb-frontend-attr-a1-5b5757c6c4-4q79d:/home/ezollug/work/kind# ss -lpu
State            Recv-Q           Send-Q                              Local Address:Port                      Peer Address:Port           Process                                       
UNCONN           0                0                                         0.0.0.0:3784                           0.0.0.0:*               users:(("bird",pid=1836951,fd=12))           
UNCONN           0                0                          169.254.100.2%eth0.100:49641                          0.0.0.0:*               users:(("bird",pid=1836951,fd=18))           
UNCONN           0                0                           [100:100::2]%eth0.100:60464                             [::]:*               users:(("bird",pid=1836951,fd=15))           
UNCONN           0                0                                            [::]:3784                              [::]:*               users:(("bird",pid=1836951,fd=13)) 

Issue link

NA

Checklist

• Purpose
  • Bug fix
  • New functionality
  • Documentation
  • Refactoring
  • CI
• Test
  • Unit test
  • E2E Test
  • Tested manually
• Introduce a breaking change
  • Yes (description required)
  • No