slirp/smb: Move ncalrpc directory to tmp

The smbd forked by qemu still uses the default ncalrpc directory
in /var/run/samba. This may lead to problems, if /var/run/samba
does not exist (for example if /var/run is a tmpfs and the host
smbd was not started).

This leads to the following error message from samba
and an unworkable smbd:
	Failed to create pipe directory /var/run/samba/ncalrpc - No such file or directory

Fix this by pointing smbd to /tmp/qemu-smb.%d.%d/ncalrpc as ncalrpc directory.
Smbd will create the actual ncalrpc subdirectory on its own.
Signed-off-by: NMichael Buesch <m@bues.ch>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>
(Applying this to -trivial because it _is_ rather trivial
 and because Jan does not reply for months)

net/slirp.c

@@ -527,6 +527,7 @@ static int slirp_smb(SlirpState* s, const char *exported_dir,
             "pid directory=%s\n"
             "lock directory=%s\n"
             "state directory=%s\n"
+            "ncalrpc dir=%s/ncalrpc\n"
             "log file=%s/log.smbd\n"
             "smb passwd file=%s/smbpasswd\n"
             "security = user\n"
@@ -542,6 +543,7 @@ static int slirp_smb(SlirpState* s, const char *exported_dir,
             s->smb_dir,
             s->smb_dir,
             s->smb_dir,
+            s->smb_dir,
             exported_dir,
             passwd->pw_name
             );