Fix qemu endless loop when raising a SIGSEGV/SIGBUS signal with gdbstub in user emulation

When a SIGSEGV signal is raised in user mode emulation the current
test to know whether the signal is sent by the kernel is wrong :

info->si_code == SI_KERNEL

according to /usr/include/bits/siginfo.h it should be

info->si_code > 0

Signed-off-by: Lionel Landwerlin <lionel.landwerlin@openwide.fr>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6151 c046a42c-6fe2-441c-8c8c-71466251a162
