Ensure max length of iptables chain name w/o prefix is up to 11 chars.

Ensure max length of iptables chain name w/o prefix is up to 11 chars.

The maximum length of Linux iptables chain name must be less than or
equal to 28 characters. In iptables_manager binary_name up to 16 chars
is used as a prefix and a '-' follows it, so a chain name passed to
iptables_manager must be less than 12 character long. Accordingky
MAX_CHAIN_LEN should be changed from 28 to 12. Also this commit
introduces a method to get a chain name with valid length.

Since iptables_firewall module constructs a rule by directly using
a chain name, iptable_firewall also must take care of the length.

Fixes bug #1133833

Change-Id: I6157d519f3cb91ec32dc6a92eae45439b8717b2d