[bgpd] Add support for the old Linux 2.4, TCP_MD5_AUTH RFC2385 patch

* configure.ac: Add a --enable-linux24-tcp-md5 argument, to compile in
  support for the old TCP-MD5 patch for Linux 2.4 systems.  This overrides
  auto-detection of TCP-MD5 supported by the target system.
* lib/sockopt.c: (sockopt_tcp_signature) add in a variant for the old
  Linux 2.4, TCP_MD5_AUTH variant of TCP-MD5 support, conditional
  on the previous configure arg.
2 files changed