windows: Factorize handling of DLL load address offset

windows: Factorize handling of DLL load address offset

This patch is a small cleanup that moves the magic 0x1000 offset
to apply to a DLL's base address inside the win32_add_one_solib
function, rather than delegate that reponsibility to its callers.

gdb/gdbserver/ChangeLog:

	* win32-low.c (win32_add_one_solib): Add 0x1000 to load_addr.
	Add comment.
	(win32_add_all_dlls): Remove 0x1000 offset applied to DLL
	base address when calling win32_add_one_solib.
	(handle_load_dll): Delete local variable load_addr.
	Remove 0x1000 offset applied to DLL base address when calling
	win32_add_one_solib.
	(handle_unload_dll): Add comment.