bind-server: accept any value to option.

Rather than trying to validate, accept any option to the bind-server
option, and allow mosh-server to validate it, as noted by
https://github.com/mobile-shell/mosh/pull/670#issuecomment-135147605

Fixes: 669
Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>

scripts/mosh.pl

@@ -221,11 +221,8 @@ if ( ! defined $fake_proxy ) {
     }
   } elsif ( $bind_ip =~ m{^any$}i ) {
     # do nothing
-  } elsif ( $bind_ip =~ m{^[0-9\.]+$} ) {
-    push @bind_arguments, ('-i', "$bind_ip");
   } else {
-    print STDERR qq{$0: Unknown server binding option: $bind_ip\n};
-    die $usage;
+    push @bind_arguments, ('-i', "$bind_ip");
   }
 } else {
   my ( $host, $port ) = @ARGV;