libmultipath: Improve debugging of log messages

libmultipath: Improve debugging of log messages

With the current definition of log messages we
only see something utterly pointless when using
gdb:
(gdb) print *(struct logmsg *)la->buff
$15 = {prio = 6, next = 0x80015a68,
  str = 0x73687574646f776e <Address 0x73687574646f776e out of bounds>}

With this fix we are able to see the message
directly:

(gdb) print *(struct logmsg *)la->buff
$6 = {prio = 5, next = 0x8001b220,
  str = 0x8001d240 "--------shut down-------\n"}

References: bnc#659859

Signed-off-by: Hannes Reinecke <hare@suse.de>