backport support for ipv6 for older glibc

CMakeLists.txt

@@ -81,6 +81,7 @@ option(ENABLE_MSAN     "Enable clang memory sanitizer"            OFF)
 option(ENABLE_TIDY     "Enable clang tidy"                        OFF)
 
 option(USE_LTE_RATES   "Use standard LTE sampling rates"          OFF)
+option(USE_GLIBC_IPV6  "Use glibc's own ipv6.h"                   ON)
 
 set(GCC_ARCH native CACHE STRING "GCC compile for specific architecture.")
 
@@ -301,6 +302,11 @@ if(CMAKE_C_COMPILER_ID MATCHES "GNU" OR CMAKE_C_COMPILER_ID MATCHES "Clang")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DFORCE_STANDARD_RATE")
   endif (USE_LTE_RATES)
 
+  if (USE_GLIBC_IPV6)
+    message(STATUS "Using default glibc header for IPv6 support.")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DUSE_GLIBC_IPV6")
+  endif (USE_GLIBC_IPV6)
+
   find_package(SSE)
   if (HAVE_AVX2)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=${GCC_ARCH} -mfpmath=sse -mavx2 -DLV_HAVE_AVX2 -DLV_HAVE_AVX -DLV_HAVE_SSE")

srsue/src/upper/gw.cc

@@ -24,15 +24,47 @@
 #include <errno.h>
 #include <unistd.h>
 #include <fcntl.h>
-#include <arpa/inet.h>
 #include <linux/ip.h>
-#include <linux/ipv6.h>
 #include <linux/if_tun.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>
 
+#ifdef USE_GLIBC_IPV6
+#include <linux/ipv6.h>
+#else
+// Some versions of glibc yield to a compile error with gcc
+// complaining about a redefinition of struct in6_pktinfo. See [1].
+// Since we only need two structs from that header we define them here and
+// just don't include the entire file. See [1] for more information.
+//
+// [1] https://patchwork.ozlabs.org/patch/425881/
+struct ipv6hdr {
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+  __u8 priority : 4, version : 4;
+#elif defined(__BIG_ENDIAN_BITFIELD)
+  __u8 version : 4, priority : 4;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+  __u8 flow_lbl[3];
+
+  __be16 payload_len;
+  __u8   nexthdr;
+  __u8   hop_limit;
+
+  struct in6_addr saddr;
+  struct in6_addr daddr;
+};
+
+struct in6_ifreq {
+  struct in6_addr ifr6_addr;
+  __u32           ifr6_prefixlen;
+  int             ifr6_ifindex;
+};
+#endif
+
 namespace srsue {
 
 gw::gw()