log: make log_set_upgrade_syslog_to_journal() take effect immediately

This doesn't matter much, and we don't rely on it, but I think it's much
nicer if we log_set_target() and log_set_upgrade_syslog_to_journal() can
be called in either order and have the same effect.

src/basic/log.c

@@ -1314,6 +1314,14 @@ int log_syntax_invalid_utf8_internal(
 
 void log_set_upgrade_syslog_to_journal(bool b) {
         upgrade_syslog_to_journal = b;
+
+        /* Make the change effective immediately */
+        if (b) {
+                if (log_target == LOG_TARGET_SYSLOG)
+                        log_target = LOG_TARGET_JOURNAL;
+                else if (log_target == LOG_TARGET_SYSLOG_OR_KMSG)
+                        log_target = LOG_TARGET_JOURNAL_OR_KMSG;
+        }
 }
 
 void log_set_always_reopen_console(bool b) {

src/basic/log.h

@@ -302,6 +302,7 @@ LogTarget log_target_from_string(const char *s) _pure_;
 
 void log_received_signal(int level, const struct signalfd_siginfo *si);
 
+/* If turned on, any requests for a log target involving "syslog" will be implicitly upgraded to the equivalent journal target */
 void log_set_upgrade_syslog_to_journal(bool b);
 void log_set_always_reopen_console(bool b);
 void log_set_open_when_needed(bool b);