wc(1): Fix 'wc -L'

I inadvertently broke 'wc -L' in r326736. We must skip the fast path if -L
was specified, in addition to the existing check for the -l option.

Document long-standing -L behavior (count varies depending on whether wc(1)
is run with the -m option or not) in wc.1. That behavior dates back to the
introduction of the -L option, but was not documented.

PR: 230300
Reported by: <amstrnad+bugzilla AT gmail.com>
Sponsored by: Dell EMC Isilon