Rename module netdb to netdb-h. * modules/netdb-h: Renamed from modules/netdb. * modules/netdb-h-tests: Renamed from modules/netdb-tests. * modules/netdb-h-c++-tests: Renamed from modules/netdb-c++-tests. * tests/test-netdb-h.c: Renamed from tests/test-netdb.c. * tests/test-netdb-h-c++.cc: Renamed from tests/test-netdb-c++.cc. * doc/posix-headers/netdb.texi: Update. * modules/* (Depends-on): Update. * modules/netdb: New file.