[linux] Add command line arguments

Support qemu-like arguments for network setup:
--net driver_name[,setting=value]*

and global settings:
--settings setting=value[,setting=value]*

Signed-off-by: Piotr Jaroszyński <p.jaroszynski@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/prefix/linuxprefix.S

@@ -16,6 +16,9 @@ _start:
 	pushl	%edi // argv -> C arg2
 	pushl	%esi // argc -> C arg1
 
+	call	save_args
+
+	/* Our main doesn't use any arguments */
 	call	main
 
 	movl	%eax, %ebx // rc -> syscall arg1

src/arch/x86_64/prefix/linuxprefix.S

@@ -13,6 +13,9 @@ _start:
 
 	andq	$~15, %rsp // 16-byte align the stack
 
+	call	save_args
+
+	/* Our main doesn't use any arguments */
 	call	main
 
 	movq	%rax, %rdi // rc -> syscall arg1