Look up an environment variable and convert the stored address. If the address
is valid, then the function returns 1. Otherwise, the function returns 0. In
all cases, the enetaddr memory is initialized. If the env var is not found,
Look up an environment variable and convert the stored address. If the address
is valid, then the function returns 1. Otherwise, the function returns 0. In
all cases, the enetaddr memory is initialized. If the env var is not found,