snmpd: instead option -LS by -Ls

Option -LS does not work, we should instead it by -Ls as usage said.

 Deprecated options:
   -l FILE               use -Lf <FILE> instead
   -P                    use -p instead
   -s                    use -Lsd instead
   -S d|i|0-7            use -Ls <facility> instead

Signed-off-by: Bian Naimeng <biannm@cn.fujitsu.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>