Description: Fix gcc-7 compile errors

 * Fix comparison between pointer and zero character constant.

 * Fix implicit fallthrough by adding a break (though the break will never be

   reached since exit is called anyways).

 * Add fallthrough comment where fallthrough is intentional.  Gcc parses this

   comment and recognizes the fallthrough as intentional.

Author: Lukas Schwaighofer <lukas@schwaighofer.name>

--- a/src/opt.c

+++ b/src/opt.c

@@ -222,6 +222,7 @@

                 /* Print the version command option, cleanup and exit. */

                 std_version();

                 exit_cleanup(true);

+                break;

             case 'h':

                 MSG_DEBUG("-h or --help command option");

@@ -229,6 +230,7 @@

                 /* Print the help screen command option, cleanup and exit. */

                 std_help();

                 exit_cleanup(true);

+                break;

             case '?':

             case ':':

@@ -285,8 +287,8 @@

     }

     /* Re-initialize the interface name command option to no interface? */

-    if (opt->interface != '\0')

-        memset(opt->interface, '\0', (size_t)IF_NAMESIZE);

+    if (opt->interface != NULL)

+        memset(opt->interface, 0, (size_t)IF_NAMESIZE);

     /* Set the value of the interface name command option. */

     memcpy(opt->interface, interface, len);

--- a/src/sig.c

+++ b/src/sig.c

@@ -204,6 +204,7 @@

             case SIGINT:

                 /* Remove ^C symbol from the output terminal. */

                 printf("\r");

+		/* FALLTHRU */

             case SIGTERM:

                 MSG_DEBUG("Caught %s (%d)..", SIG_ITOA(sig), sig);