ipv6_unicast construct error

[cs948294549]

yabgp/yabgp/message/attribute/nlri/ipv6_unicast.py

Line 63 in f073633

nlri_hex += binascii.unhexlify(hex(prefix.ip)[2:])

length of prefix is variable,
nlri_hex += binascii.unhexlify(hex(prefix.ip)[2:math.ceil(prefix.prefixlen / 8)*2+2])
eg.
2001:db8::/40

1 2 3 4 5 6
40 20 01 0d b8 0
1 byte for length, math.ceil(40/8) = 5byte for prefix