Simplify port to musl libc

[marekm72]

Looking at the recent changes to build accel-ppp for Alpine Linux which uses musl libc instead of glibc, I see they can be cleaned up a little - see below for proposed patch. Instead of extra logic to detect good linux/if_arp.h include the correct one net/if_arp.h available on both platforms. Remove check and use of __free_fn_t and make the code compatible with both musl and glibc with no changes. Remove check and use of printf.h which is not needed at all.

Tested to build on Debian 12.7 and Alpine 3.20.3. Please review, and test on any other platforms that may need to be supported but I couldn't test easily, like OpenWrt. Please bear with me using patches not PRs as it's easier for me that way - thanks!

diff --git a/accel-pppd/CMakeLists.txt b/accel-pppd/CMakeLists.txt
index 496fbdc..5d4fa28 100644
--- a/accel-pppd/CMakeLists.txt
+++ b/accel-pppd/CMakeLists.txt
@@ -44,33 +44,6 @@ IF (RADIUS)
 	ADD_SUBDIRECTORY(radius)
 ENDIF (RADIUS)
 
-# define __free_fn_t in musl
-INCLUDE (CheckCSourceCompiles)
-CHECK_C_SOURCE_COMPILES("
-#include <stdlib.h>
-#include <search.h>
-int main(void)
-{
-	__free_fn_t *f;
-	return 0;
-}" HAVE_FREE_FN_T)
-IF (HAVE_FREE_FN_T)
-	ADD_DEFINITIONS(-DHAVE_FREE_FN_T)
-ENDIF (HAVE_FREE_FN_T)
-
-INCLUDE (CheckCSourceCompiles)
-CHECK_C_SOURCE_COMPILES("
-#include <linux/if_arp.h>
-#include <net/ethernet.h>
-int main(void)
-{
-	return 0;
-}" HAVE_GOOD_IFARP)
-
-IF (HAVE_GOOD_IFARP)
-	ADD_DEFINITIONS(-DHAVE_GOOD_IFARP)
-ENDIF (HAVE_GOOD_IFARP)
-
 INCLUDE (CheckCSourceCompiles)
 CHECK_C_SOURCE_COMPILES("
 #include <utmp.h>
@@ -103,12 +76,6 @@ ENDIF (SHAPER)
 
 INCLUDE(CheckIncludeFile)
 CHECK_INCLUDE_FILE("linux/netfilter/ipset/ip_set.h" HAVE_IPSET)
-# MUSL does not have printf.h
-CHECK_INCLUDE_FILE("printf.h" HAVE_PRINTF_H)
-IF (HAVE_PRINTF_H)
-	ADD_DEFINITIONS(-DHAVE_PRINTF_H)
-ENDIF (HAVE_PRINTF_H)
-
 
 INCLUDE(CheckFunctionExists)
 CHECK_FUNCTION_EXISTS(setns HAVE_SETNS)
diff --git a/accel-pppd/ctrl/ipoe/arp.c b/accel-pppd/ctrl/ipoe/arp.c
index ef9d385..a6ca5b1 100644
--- a/accel-pppd/ctrl/ipoe/arp.c
+++ b/accel-pppd/ctrl/ipoe/arp.c
@@ -13,10 +13,8 @@
 #include <netinet/ip.h>
 #include <sys/socket.h>
 #include <sys/ioctl.h>
-#ifdef HAVE_GOOD_IFARP
-#include <linux/if_arp.h>
-#endif
-#include <linux/if_packet.h>
+#include <net/if_arp.h>
+#include <netpacket/packet.h>
 
 #include "list.h"
 #include "triton.h"
diff --git a/accel-pppd/ctrl/ipoe/ipoe.c b/accel-pppd/ctrl/ipoe/ipoe.c
index 206d0f8..5c9bb82 100644
--- a/accel-pppd/ctrl/ipoe/ipoe.c
+++ b/accel-pppd/ctrl/ipoe/ipoe.c
@@ -14,11 +14,9 @@
 #include <netinet/ip.h>
 #include <sys/socket.h>
 #include <sys/ioctl.h>
-#include <linux/if.h>
-#ifdef HAVE_GOOD_IFARP
-#include <linux/if_arp.h>
-#endif
-#include <linux/route.h>
+#include <net/if.h>
+#include <net/if_arp.h>
+#include <net/route.h>
 
 #include <pcre.h>
 
diff --git a/accel-pppd/ctrl/l2tp/l2tp.c b/accel-pppd/ctrl/l2tp/l2tp.c
index 01cea2d..ea5d30b 100644
--- a/accel-pppd/ctrl/l2tp/l2tp.c
+++ b/accel-pppd/ctrl/l2tp/l2tp.c
@@ -848,16 +848,17 @@ out_err:
 	return -1;
 }
 
+static void l2tp_session_free_ptr(void *ptr)
+{
+	l2tp_session_free((struct l2tp_sess_t *) ptr);
+}
+
 static void l2tp_tunnel_free_sessions(struct l2tp_conn_t *conn)
 {
 	void *sessions = conn->sessions;
 
 	conn->sessions = NULL;
-#ifdef HAVE_FREE_FN_T
-	tdestroy(sessions, (__free_fn_t)l2tp_session_free);
-#else
-	tdestroy(sessions, (void(*)(void *))l2tp_session_free);
-#endif
+	tdestroy(sessions, l2tp_session_free_ptr);
 	/* Let l2tp_session_free() handle the session counter and
 	 * the reference held by the tunnel.
 	 */
diff --git a/accel-pppd/ctrl/pppoe/pppoe.c b/accel-pppd/ctrl/pppoe/pppoe.c
index 8678db8..620691d 100644
--- a/accel-pppd/ctrl/pppoe/pppoe.c
+++ b/accel-pppd/ctrl/pppoe/pppoe.c
@@ -11,9 +11,6 @@
 #include <net/ethernet.h>
 #include <netpacket/packet.h>
 #include <arpa/inet.h>
-#ifdef HAVE_PRINTF_H
-#include <printf.h>
-#endif
 
 #include "crypto.h"