lldp: add option/command to override hostname

Allow to override the system name (hostname) by using '-N' as parameter to
lldpd, or by using "configure system hostname <NAME>" to lldpcli.

Signed-off-by: Jonas Johansson <jonasj76@gmail.com>
lldpd: Remove the '-N' command-line flag

Too many flags being added, use of configuration file is prefered.

Signed-off-by: Jonas Johansson <jonasj76@gmail.com>
Merge pull request #60 from jonasj76/override-hostname

lldp: add option/command to override hostname
lldpd: add a note about command-line options

lldpcli should be preferred for new options.