[syslog5424] confirm process ID is nil when RFC NILVALUE used
[syslog5424] structured data should be nil when RFC NILVALUE is used
[syslog5424] do not capture chevrons with priority value

Priority is "191", not "<191>".  The syslog_pri filter expects a
raw integer without the extra punctuation.
[syslog5424] non-capturing parens since no backreferences needed