procd: mdns: Support txt values with spaces

procd: mdns: Support txt values with spaces

Properly quote the arguments so that you can register a service with TXT
entries that contains spaces.

Example:
   procd_add_mdns myservice tcp 9999 "key=descriptive text field 1" \
         "another=something equally verbose"

Output before:
$ avahi-browse -r -v _myservice._tcp
_myservice._tcp      local
   hostname = [blah.local]
   address = [192.168.255.74]
   port = [9999]
   txt = ["verbose" "equally" "another=something" "1" "field" "text" "key=descriptive"]

Output now:
$ avahi-browse -r -v _myservice._tcp
_myservice._tcp      local
   hostname = [blah.local]
   address = [192.168.255.74]
   port = [9999]
   txt = ["another=something equally verbose" "key=descriptive text field 1"]

Signed-off-by: Karl Palsson <karlp@etactica.com>