logger: allow use of --id=ppid when logging locally

There is no obvious way to make syslog(3) to print both pid or ppid, so
duplicate the libc syslog() to logger.  Making the ppid printing work
using unix socket has side effect of local becoming capable to use both
rfc format output, which is hopefully seen as good thing.  The
syslog_local() is format wise one-to-one copy with glibc syslog(3)
format.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
logger: remove openlog(3) options

One variable less, and more importantly bit operations become unnecessary
in if statements.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
logger: optimize string initializations

Setting whole array to be completely full of nulls cannot be as quick as
making the only significant member of the array when needed.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
logger: set function arguments read-only when possible

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
docs: mentintion default udp and tcp ports logger is using

The fact that 'syslog tcp/514' does not exist in RFS's, which has lead
to 'syslog-conn 601/tcp' be used in place could be a suprice and should
be told in manual.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
Merge remote-tracking branch 'sami/logger'
logger: use generic --id=<id>

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