slirp: Add domainname option to slirp's DHCP server

This patch will allow the user to include the domainname option in
replies from the built-in DHCP server.

Signed-off-by: Benjamin Drung <benjamin.drung@profitbricks.com>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
diff --git a/qemu-options.hx b/qemu-options.hx
index 2f61ea4..c0d3951 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1906,8 +1906,8 @@
     "-netdev user,id=str[,ipv4[=on|off]][,net=addr[/mask]][,host=addr]\n"
     "         [,ipv6[=on|off]][,ipv6-net=addr[/int]][,ipv6-host=addr]\n"
     "         [,restrict=on|off][,hostname=host][,dhcpstart=addr]\n"
-    "         [,dns=addr][,ipv6-dns=addr][,dnssearch=domain][,tftp=dir]\n"
-    "         [,bootfile=f][,hostfwd=rule][,guestfwd=rule]"
+    "         [,dns=addr][,ipv6-dns=addr][,dnssearch=domain][,domainname=domain]\n"
+    "         [,tftp=dir][,bootfile=f][,hostfwd=rule][,guestfwd=rule]"
 #ifndef _WIN32
                                              "[,smb=dir[,smbserver=addr]]\n"
 #endif
@@ -2135,6 +2135,9 @@
 qemu-system-i386 -nic user,dnssearch=mgmt.example.org,dnssearch=example.org
 @end example
 
+@item domainname=@var{domain}
+Specifies the client domain name reported by the built-in DHCP server.
+
 @item tftp=@var{dir}
 When using the user mode network stack, activate a built-in TFTP
 server. The files in @var{dir} will be exposed as the root of a TFTP server.