journal/kmsg: drop Server.dev_kmsg_readable flag and use Server.read_kmsg

When /dev/kmsg is opened, the two flags have the same value.

This also adds an assertion in server_read_dev_kmsg().

src/journal/journald-kmsg.c

@@ -320,6 +320,7 @@ static int server_read_dev_kmsg(Server *s) {
 
         assert(s);
         assert(s->dev_kmsg_fd >= 0);
+        assert(s->read_kmsg);
 
         l = read(s->dev_kmsg_fd, buffer, sizeof(buffer) - 1);
         if (l == 0)
@@ -343,7 +344,7 @@ int server_flush_dev_kmsg(Server *s) {
         if (s->dev_kmsg_fd < 0)
                 return 0;
 
-        if (!s->dev_kmsg_readable)
+        if (!s->read_kmsg)
                 return 0;
 
         log_debug("Flushing /dev/kmsg...");
@@ -406,7 +407,6 @@ int server_open_dev_kmsg(Server *s) {
                 goto finish;
         }
 
-        s->dev_kmsg_readable = true;
         return 0;
 
 finish:
@@ -423,7 +423,7 @@ int server_open_kernel_seqnum(Server *s) {
         /* We store the seqnum we last read in an mmapped file. That way we can just use it like a variable,
          * but it is persistent and automatically flushed at reboot. */
 
-        if (!s->dev_kmsg_readable)
+        if (!s->read_kmsg)
                 return 0;
 
         r = server_map_seqnum_file(s, "kernel-seqnum", sizeof(uint64_t), (void**) &s->kernel_seqnum);

src/journal/journald-server.h

@@ -154,7 +154,6 @@ struct Server {
         Set *deferred_closes;
 
         uint64_t *kernel_seqnum;
-        bool dev_kmsg_readable:1;
         RateLimit kmsg_own_ratelimit;
 
         bool send_watchdog:1;