container.conf: Fix off by 2 in option parsing

This commit fixes a off by 2 in config option parsing
(due to missing parenthesis). The error occurs if for instance
lxc.net.0.type is parsed. In that case, the .0 is removed from the
string. However, due to the missing parenthesis, the null terminating
character is off by two which means the modified config option would
be lxc.net.typepe instead of lxc.net.type.

Signed-off-by: Maximilian Blenk <Maximilian.Blenk@bmw.de>

src/lxc/confile.c

@@ -4240,7 +4240,7 @@ static struct lxc_config_t *get_network_config_ops(const char *key,
 		}
 
 		memmove(copy + 8, idx_end + 1, strlen(idx_end + 1));
-		copy[strlen(key) - numstrlen + 1] = '\0';
+		copy[strlen(key) - (numstrlen + 1)] = '\0';
 
 		config = lxc_get_config(copy);
 		if (!config) {