Update config.mk

Adding IPv6 flag to enable IPv6 support in the library.
Update applemidi.c

Added support for IPv6 connections.
Update osc.c

Adding support for IPv6 connections.
Update Makefile

Adding 2 test cases for IPv6 connection testing.
Create driver_applemidiv6.c

Testing applemidi drivers for IPv6 connections.
Create driver_rtpv6.c

Testing rtp driver for IPv6 connections.
Fix some typos around the #ifdefs
Merge commit 'refs/pull/11/head' into ipv6

* commit 'refs/pull/11/head':
  Update osc.c
  Update port.c
  Update rtp.c
  Update osc.c
Fix missing dependencies
De-duplicate socket creation & binding
De-duplicate binding
Allow setting USE_IPV6 without touching config.mk

Use `make USE_IPV6=0` to build without ipv6 support.
Less ifs
Merge branch 'ipv6'

* ipv6:
  Less ifs
  Allow setting USE_IPV6 without touching config.mk
  De-duplicate binding
  De-duplicate socket creation & binding
  Fix missing dependencies
  Fix some typos around the #ifdefs
  Create driver_rtpv6.c
  Create driver_applemidiv6.c
  Update Makefile
  Update osc.c
  Update applemidi.c
  Update config.mk