Include sys/types.h for u_int8_t and define _GNU_SOURCE for musl to
expose it.
Fixes: 54802b2c2826 ("Report if the option is supported by a newer kernel release") Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be> Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>