x86: exception during hardware interrupt pushes wrong error code
Description of problem:
Exceptions during IDT traversal push the wrong error code when triggered by a hardware interrupt.
The EXT bit in TCG mode is never set.  However, it works fine in KVM mode as hardware is generating the number.
Steps to reproduce:
1. load a short IDT e.g. with 64 entries
2. trigger a self IPI through the LAPIC with a vector 100
3. the pushed error code is 802 instead of 803.
Additional information:
It can be fixed in the lines `raise_exception_err(env, EXCP0D_GPF, intno * 8 + 2);` in `seg_helper.c` 
which must include the `is_hw` field when calculating the error number. Something like `intno * 8 + 2 + (is_hw != 0)` 
works here.

Nevertheless, all the other exception cases in the `do_interrupt_*` functions have to set the same bit as well.