shairport-sync: Enable pipe audio backend support

UCI's shairport-sync's pipe conf block is defined but has no effect without shairport-sync's pipe support

Rationale for pipe support:
- On SBC with no sound card available (built-in or external)
  and without ALSA plugins support on OpenwRT (no package)
  to reroute a stream from shairport-sync's ALSA default output
  to a PulseAudio controlled Bluetooth sink , then pipe support
  is required to enable the following flow:
  - shairport-sync -> fifo pipe -> custom_binary_to_send_stream_to_pulse_audio_BT_sink
- small bump in package size: diff: +746 bytes
  - shairport-sync-openssl_4.3.2-0_aarch64_generic.ipk without --pipe: 110806 bytes
  - shairport-sync-openssl_4.3.2-0_aarch64_generic.ipk with --pipe: 111552 bytes

Signed-off-by: David Andreoletti <david@andreoletti.net>

sound/shairport-sync/Makefile

@@ -8,7 +8,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=shairport-sync
 PKG_VERSION:=4.3.2
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://codeload.github.com/mikebrady/shairport-sync/tar.gz/$(PKG_VERSION)?
@@ -79,6 +79,7 @@ CONFIGURE_ARGS += \
 	--with-alsa \
 	--with-libdaemon \
 	--with-airplay-2 \
+	--with-pipe \
 	--with-metadata
 
 ifeq ($(BUILD_VARIANT),openssl)