quagga: option "-z" ("--socket <path>") added

All daemons modified to support custom path to zserv
socket.

lib: generalize a zclient connection

zclient_socket_connect added. zclient_socket and
zclient_socket_un were hidden under static expression.
"zclient_serv_path_set" modified.
diff --git a/ospf6d/ospf6_main.c b/ospf6d/ospf6_main.c
index ced2ef2..235a685 100644
--- a/ospf6d/ospf6_main.c
+++ b/ospf6d/ospf6_main.c
@@ -77,6 +77,7 @@
   { "daemon",      no_argument,       NULL, 'd'},
   { "config_file", required_argument, NULL, 'f'},
   { "pid_file",    required_argument, NULL, 'i'},
+  { "socket",      required_argument, NULL, 'z'},
   { "vty_addr",    required_argument, NULL, 'A'},
   { "vty_port",    required_argument, NULL, 'P'},
   { "user",        required_argument, NULL, 'u'},
@@ -115,6 +116,7 @@
 -d, --daemon       Runs in daemon mode\n\
 -f, --config_file  Set configuration file name\n\
 -i, --pid_file     Set process identifier file name\n\
+-z, --socket       Set path of zebra socket\n\
 -A, --vty_addr     Set vty's bind address\n\
 -P, --vty_port     Set vty's port number\n\
 -u, --user         User to run as\n\
@@ -202,7 +204,7 @@
   /* Command line argument treatment. */
   while (1) 
     {
-      opt = getopt_long (argc, argv, "df:i:hp:A:P:u:g:vC", longopts, 0);
+      opt = getopt_long (argc, argv, "df:i:z:hp:A:P:u:g:vC", longopts, 0);
     
       if (opt == EOF)
         break;
@@ -223,6 +225,9 @@
         case 'i':
           pid_file = optarg;
           break;
+        case 'z':
+          zclient_serv_path_set (optarg);
+          break;
         case 'P':
          /* Deal with atoi() returning 0 on failure, and ospf6d not
              listening on ospf6d port... */