[GSO] Added comments to block #ifdef...#endif
[GSO-core] Added comments to block #ifdef...#endif and removed useless code
[GSO] Added block #ifdef...#endif in each "#include <net/gso.h>"
[GSO-tcp_output] Fix comment mistake
[GSO-ether_output] Stored the eth hdr len in a local variable.
[GSO-ip_output/ip6_output] Removed some #ifdef...#endif blocks for readability.
[GSO-ip_output] Removed TSO checksum fix (created different patch)