[PATCH] musl: fix conflict on ethhdr definition

[Laurent Vivier <lvivier@redhat.com>]

there is a conflict between netinet/if_ether.h provided by musl and
linux/if_ether.h provided by the linux headers:

  In file included from passt.h:185,
                   from tcp_vu.c:21:
  /usr/include/netinet/if_ether.h:115:8: error: redefinition of 'struct ethhdr'
    115 | struct ethhdr {
        |        ^~~~~~
  In file included from /usr/include/linux/virtio_net.h:32,
                   from tcp_vu.c:17:
  /usr/include/linux/if_ether.h:173:8: note: originally defined here
    173 | struct ethhdr {
        |        ^~~~~~

The kernel headers provide a flag to disable the definition in this case,
__UAPI_DEF_ETHHDR (see /usr/include/linux/if_ether.h comment).

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Makefile b/Makefile
index cb7448079de5..2aa56ada65fd 100644
--- a/Makefile
+++ b/Makefile
@@ -33,6 +33,9 @@ FLAGS +=  $(FORTIFY_FLAG) -O2 -pie -fPIE
 FLAGS += -DPAGE_SIZE=$(shell getconf PAGE_SIZE)
 FLAGS += -DVERSION=\"$(VERSION)\"
 FLAGS += -DDUAL_STACK_SOCKETS=$(DUAL_STACK_SOCKETS)
+ifeq (musl, $(word 4,$(subst -, ,$(TARGET))))
+FLAGS += -D__UAPI_DEF_ETHHDR=0
+endif
 
 PASST_SRCS = arch.c arp.c checksum.c conf.c dhcp.c dhcpv6.c flow.c fwd.c \
 	icmp.c igmp.c inany.c iov.c ip.c isolation.c lineread.c log.c mld.c \
-- 
@@ -33,6 +33,9 @@ FLAGS +=  $(FORTIFY_FLAG) -O2 -pie -fPIE
 FLAGS += -DPAGE_SIZE=$(shell getconf PAGE_SIZE)
 FLAGS += -DVERSION=\"$(VERSION)\"
 FLAGS += -DDUAL_STACK_SOCKETS=$(DUAL_STACK_SOCKETS)
+ifeq (musl, $(word 4,$(subst -, ,$(TARGET))))
+FLAGS += -D__UAPI_DEF_ETHHDR=0
+endif
 
 PASST_SRCS = arch.c arp.c checksum.c conf.c dhcp.c dhcpv6.c flow.c fwd.c \
 	icmp.c igmp.c inany.c iov.c ip.c isolation.c lineread.c log.c mld.c \
-- 
2.47.0