logger: use --id as local socket credentials

logger: use --id as local socket credentials

If you have really paranoid syslog (or systemd who listens on /dev/log)
then it replaces in the message PID with a real PID from socket header
credentials:

 # echo $PPID
 1550

 # logger -p info --stderr --id=$PPID "This is message baby!"
 <14>Oct 29 11:22:13 kzak[1550]: This is message baby!

 # journald -n 1
 Oct 29 11:22:13 ws kzak[22100]: This is message baby!
                         ^^^^^

This patch forces kernel to accept another *valid* PID if logger(1)
executed with root permissions; improved version:

 # logger -p info --stderr --id=$PPID "This is message baby!"
 <14>Oct 29 11:26:00 kzak[1550]: This is message baby!

 # journald -n 1
 Oct 29 11:26:00 ws kzak[1550]: This is message baby!

Signed-off-by: Karel Zak <kzak@redhat.com>