cmake HAVE_LINUX_NET_TSTAMP_H examples

CTSRD-CHERI/cheribsd contrib/libpcap/CMakeLists.txt :2239 

check_include_file(linux/net_tstamp.h HAVE_LINUX_NET_TSTAMP_H)

asset-group/5ghoul-5g-nr-attacks libs/libpcap/CMakeLists.txt :1473 

check_include_file(linux/net_tstamp.h HAVE_LINUX_NET_TSTAMP_H)