add support for vlan-advertisements configuration (#740)

add support for vlan-advertisements configuration (#740)

* add support for vlan-advertisements configuration

adding new configurations configure [ports ethx [,..]] lldp vlan-advertisements pattern and
unconfigure [ports ethx,[,...]] lldp vlan-advertisements pattern.
The commands enable control of which vlans are advertised

* Code review changes

Updated manual page.
Added add an example of invocation in tests/lldpcli.conf.
Added tests to tests/integration/test_dot1.py.
Vlan formatting fixes.

* more CR fixes

* Fix memory leak

fixing port->p_vlan_advertise_pattern memory leak