adb: Win32: set socket buffer sizes properly

On Windows, adb_socket_setbufsize() was taking a file descriptor value
from the compatibility layer in sysdeps_win32.c (namely, an index into
the _win32_fhs array) and passing it to the Winsock setsockopt() call,
which wants a Winsock SOCKET handle. Basically, adb_socket_setbufsize()
was passing `fd` instead of `_fh_from_int(fd)->fh_socket`, resulting in
adb effectively setting a socket buffer size on a random socket in the
process.

The fix is to introduce adb_setsockopt() which just calls setsockopt()
on non-Win32, and which uses the Winsock SOCKET handle on Win32. The
change also moves Win32 disable_tcp_nagle() to a header and adds an
extra sanity check to adb_shutdown().

Change-Id: I4354e818d27538f7ff5b0e70b28bdb6300e1b98b
Signed-off-by: Spencer Low <CompareAndSwap@gmail.com>