Apply the style rule that an accessor is named similar to the the underlying value. Provide read and write accessors for each mandatory header attribute. Fix some incorrect structure in the headers like with the flags field in Ipv4_packet. Ref #2490
Thereby fix bug in the NIC router that previously used uint8_t values for ports in some places. Ref #2193
Ref #2139
Thanks Keiko Nakata for reporting! Fixes #2164
Fixes #2105