The use of TCP_ in udp.h is not known, fortunately udp.h is not specified by posix so there are no strict namespace rules, added in linux commit e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 xfrm: add espintcp (RFC 8229)
The use of TCP_ in udp.h is not known, fortunately udp.h is not specified by posix so there are no strict namespace rules, added in linux commit e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 xfrm: add espintcp (RFC 8229)