tinc: fix parsing of -b flag

[Todd C. Miller]

Only the short -b option is missing, --batch works as expected.

 - todd

diff --git a/src/tincctl.c b/src/tincctl.c
index 9eb9a1b..766b769 100644
--- a/src/tincctl.c
+++ b/src/tincctl.c
@@ -168,7 +168,7 @@ static bool parse_options(int argc, char **argv) {
 	int r;
 	int option_index = 0;
 
-	while((r = getopt_long(argc, argv, "+c:n:", long_options, &option_index)) != EOF) {
+	while((r = getopt_long(argc, argv, "+bc:n:", long_options, &option_index)) != EOF) {
 		switch (r) {
 			case 0:   /* long option */
 				break;