move the flag mappings displayed by "route show" from netstat(1) to route(8):

move the flag mappings displayed by "route show" from netstat(1) to route(8):
diff from paul tagliamonte, who was surprised to find them not documented
in route(8);

claudio agreed placement was not ideal;
deraadt confirmed users better served by route(8) than netstat(1);

i've tweaked some of the spacing and text so it displays better,
and removed some macros incorrectly associated with the "nameserver"
list item, which was messing up the formatting. should display better
now