added GRE related extensions to rofl-pipeline
new experimental extension: GRE => gre_actions and gre_matches
fixing typo in GRE extensions
fixed error in of1x_match_pp.h in function __of1x_check_match() => OF1X_MATCH_GRE_VERSION is a uint16_t value
of1x_action.c => corrected bug in functions of1x_init_match_gre_version() and of1x_init_match_gre_prot_type() => missing mapping to network byte order
of1x_match.c => function __of1x_dump_matches() => dump GRE_VERSION as hexadecimal value
of1x_match.c => function __of1x_dump_matches() => dump GRE_VERSION as hexadecimal value