add library "net" and sample script samples/network/tcp_ipaddr.kp

Sample script: tcp_ipaddr.kp
print source and destination IP address of received tcp message.

Registered net library functions:
net.ip_sock_saddr
net.ip_sock_daddr
net.format_ip_addr

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
correct a English clerical mistake in ktap_types.h

Brandon Philips: "into the" would make it even better
Edit tutorial

There are no big changes. Mostly spelling and grammar corrections.
Some parts were edited slightly for more idiomatic English.