Apply the first step of the new way to fetch data with bounds checking

Apply the first step of the new way to fetch data with bounds checking

Add GET_{BE|HE|LE}_, GET_U_1, GET_S_1, GET_IPV4_TO_HOST_ORDER,
GET_IPV4_TO_NETWORK_ORDER macros and
get_{be|he|le}_, get_u_1, get_s_1, get_ipv4_to_host_order,
get_ipv4_to_network_order inline functions,
with setjmp/longjmp logic to do better and easier data fetch with
bounds checking.

Based on Guy Harris's idea and code.