fix typo in table for getprotoent that caused out-of-bound reads

this was unlikely to lead to any crash or dangerous behavior, but
caused adjacent string constants to be treated as part of the
protocols table, possibly returning nonsensical results for unknown
protocol names/numbers or when getprotoent was called in a loop to
enumerate all protocols.
add ipv6 and icmpv6 to getprotoent-family functions

based on patch by orc.