Fixed an issue with the default parameter value.

1. By default, the init script set ip address instead of network address in the parameter value (i.e. 192.168.1.1/24 instead of 192.168.1.0/24)
2. Dynamic address were not caught by the init script

As a result, if the mynetworks parameter was left default, Postfix would have rejected the mails with the following message in the logs:

Sat Dec  6 23:26:45 2014 mail.info postfix/smtpd[22806]: NOQUEUE: reject: RCPT from unknown[104.167.106.30]: 451 4.3.0 <ds_gitcommit@shulyaka.org.ru>: Temporary lookup failure; from=<delivery@mx.sailthru.com> to=<ds_gitcommit@shulyaka.org.ru> proto=ESMTP helo=<mx-indiegogo-b.sailthru.com>
Sat Dec  6 23:26:45 2014 mail.warn postfix/smtpd[22806]: warning: non-null host address bits in "127.0.0.1/8", perhaps you should use "127.0.0.0/8" instead

This commit fixes that behavior for the new installations.

Signed-off-by: Denis Shulyaka <Shulyaka@gmail.com>