Migrate system/extra getaddrinfo test, and fix a bug in getservbyname(3).

This change is to migrate the getaddrinfo tests defined in the old file
system/extras/tests/bionic/libc/common/test_getaddrinfo.c
to the new place bionic/tests/netdb_test.cpp.

The test here is more thorough, and catches a bug in getservbyname(3)
that was breaking getaddrinfo(3)'s ability to look up services by name
without a hint that would cause it to ask for a specific protocol.

Change-Id: Ief5ebd0869496d1bc6a97861dfefa04bdf24bab1
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>