xdp-tools: fix musl build issues

xdp-tools: fix musl build issues

Add patches to fix build failures on musl-based toolchains:

0002-xdpsock-fix-struct-ethhdr-redefinition-on-musl.patch:
xdpsock.c included <net/ethernet.h> and <netinet/ether.h> alongside
<linux/if_ether.h>, triggering a struct ethhdr redefinition on musl.
Replace BSD-style ether_header/ether_addr with struct ethhdr and drop
the conflicting includes.

0003-build-use-gnu2x-to-avoid-stdbool.h-dependency.patch:
Switch CFLAGS and BPF_CFLAGS from -std=gnu11 to -std=gnu2x. In C23,
bool is a native keyword, fixing "stdbool.h: No such file or directory"
errors with a clang lacking its resource directory (e.g. llvm-bpf built
with LLVM_INSTALL_TOOLCHAIN_ONLY=ON on musl targets).

Link: https://github.com/openwrt/openwrt/pull/22983
Signed-off-by: Nick Hainke <vincent@systemli.org>