libc: use musl implementation of getifaddrs and if_nameindex

This patch replaces our home grown (possibly old musl version based)
implementation of getifaddrs() and if_nameindex() with the
implemantation of those provided by modern version musl 1.1.24 that
uses netlink interface. The advantage is that it will also support
IPV6 once we merge the ipv6 branch.

Please note that we are applying simple header trick with __netlink.h
to counter a bug in musl netlink.c. In essence the __netlink_enumerate()
in musl netlink.c calls recv() with MSG_DONTWAIT flag may (and it does
sometimes on OSv) yield EAGAIN or EWOULDBLOCK errors and there is no
error handling logic of those. Instead of adding the error handling we
change recv call to use 0 flags by re-defining MSG_DONTWAIT as 0 to
enforce blocking call which is for example what Golang runtime does
to implement similar functionality. Eventually we should try to upstream
a patch to musl.

Signed-off-by: Waldemar Kozaczuk <[email protected]>

Makefile

@@ -1503,10 +1503,12 @@ musl += network/getservbyname_r.o
 musl += network/getservbyname.o
 musl += network/getservbyport_r.o
 musl += network/getservbyport.o
-libc += network/getifaddrs.o
-libc += network/if_nameindex.o
+musl += network/getifaddrs.o
+musl += network/if_nameindex.o
 musl += network/if_freenameindex.o
 musl += network/res_init.o
+musl += network/netlink.o
+$(out)/musl/src/network/netlink.o: CFLAGS += --include libc/syscall_to_function.h --include libc/network/__netlink.h
 
 musl += prng/rand.o
 musl += prng/rand_r.o

libc/network/__netlink.h

@@ -0,0 +1,4 @@
+#include <sys/socket.h>
+#undef MSG_DONTWAIT
+//Let us disable the non-blocking call to recv() netlink.c by re-defining MSG_DONTWAIT as 0
+#define MSG_DONTWAIT 0