I'm not familiar with that module, so here's what I would have written:

sub ipv4_to_int {
    my $int = 0;
    foreach (split(/\./, $_[0]) {
        $int <<= 8;
        $int += $_;
    }
    return $int;
}

sub int_to_ipv4 {
    my $ip = '';
    my $int = shift;
    while($int) {
        $ip = ($int & 255).".$ip";
        $int >>= 8;
    }
    chop($ip);
    return $ip;
}
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Untested, season with error-checking to taste.

You hardly ever see the >> and << bit-shifting operators in perl, and bitwise AND (&) is rare too, but they behave exactly the same as they do in C.

And while I normally disapprove of "magic numbers" like the 8 and 255, I think that in this case their meaning is sufficiently obvious.