Prefix identification list. This identifies which
prefixes will match this rule. If non-null, The octet
string contains one or more 3-tuples of this form:
first octet: exact (1) or range (2)
next 16 octets: prefix
next octet: prefix length
An entry with an 'exact' tag means to only match the
specific network advertisement (prefix and length). An
entry with a 'range' tag means to match any prefix
that falls in the range indicated by the prefix and length.
An 'exact' encoding of ::0/128 means 'match the
default route. A 'range' encoding of ::0/0 means
'match any route'.
A null string also means 'match any route'.