Remove redundant GAIH_OKIFUNSPEC and GAIH_EAI.

Remove redundant GAIH_OKIFUNSPEC and GAIH_EAI.

Only gaih_inet() and gaih_inet_serv() use a special bit flag denoted
by the GAIH_OKIFUNSPEC macro. Only the return value of
gaih_inet_serv() is actively checked for the bit flag which is
redundant because it just copies the nonzero property of the value
otherwise returned. The return value of gaih_inet() is only checked
for being zero and then the bit flag is filtered out. As the bit flag
is set only for otherwise nonzero return values, it doesn't affect the
zero comparison. GAIH_EAI just an alias to ~GAIH_OKIFUNSPEC.