When setting small IPv6 block (/127), Router will get the same IP as Client

Description of problem:

When setting config-per-user with ipv6-network with a small IPv6 Block, tun device will get same ip as client side.

Version of ocserv used:

1.1.2

Client used:

AnyConnect 4.10.01075

Distributor of ocserv

Build from Release 1.1.2 from gitlab

How reproducible:

Describe the steps to reproduce the issue:

1. ocserv.conf

      auth = "plain[passwd=/etc/ocserv/passwd]"
      tcp-port = 443
      udp-port = 443
      run-as-user = nobody
      run-as-group = nogroup
      socket-file = /run/ocserv-socket
      server-cert = /var/lib/acme/vpn.xxx.net/fullchain.pem
      server-key = /var/lib/acme/vpn.xxx.net/key.pem
      keepalive = 32400
      dpd = 90
      mobile-dpd = 1800
      switch-to-tcp-timeout = 25
      try-mtu-discovery = false
      cert-user-oid = 0.9.2342.19200300.100.1.1
      tls-priorities = "NORMAL:%SERVER_PRECEDENCE:%COMPAT:-VERS-SSL3.0"
      auth-timeout = 240
      min-reauth-time = 300
      max-ban-score = 50
      ban-reset-time = 1200
      cookie-timeout = 300
      deny-roaming = false
      rekey-time = 172800
      rekey-method = ssl
      use-occtl = true
      pid-file = /run/ocserv.pid
      device = vpns
      predictable-ips = true
      default-domain = example.com
      ping-leases = false
      cisco-client-compat = true
      dtls-legacy = true
      ipv6-network = fda9:4efe:7e3b:03ea::/48
      # ipv6-subnet-prefix = 128

      config-per-user = /etc/ocserv/config-per-user/
      config-per-group = /etc/ocserv/config-per-group/

      banner = "xxxxxx"
      max-same-clients = 2
      compression = true
      no-compress-limit = 256

2. config-per-user config neverbehave

route = abcd:abcd:55:54::/64
ipv6-network = abcd:abcd:55:54:a::4/127

3. Run ocserv --foreground --pid-file /run/ocesrv.pid --config /etc/ocserv/ocserv.conf and try login

Actual results:

Both Client and Server will have IPv6 abcd:abcd:55:54:A::5 as their IP address

vpns0: flags=81<UP,POINTOPOINT,RUNNING>  mtu 1434
        inet6 fe80::20f2:be4d:32e4:88e  prefixlen 64  scopeid 0x20<link>
        inet6 2602:fc52:55:54:a::5  prefixlen 128  scopeid 0x0<global>
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 500  (UNSPEC)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 7  bytes 732 (732.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Expected results:

Client should have different IP than Router, or refuse to continue if cannot assign IP