uprobes/x86: Harden uretprobe syscall trampoline check

In the Linux kernel, the following vulnerability has been resolved:

uprobes/x86: Harden uretprobe syscall trampoline check

Jann reported a possible issue when trampoline_check_ip returns

address near the bottom of the address space that is allowed to

call into the syscall if uretprobes are not set up:

https://lore.kernel.org/bpf/202502081235.5A6F352985@keescook/T/#m9d416df341b8fbc11737dacbcd29f0054413cbbf

Though the mmap minimum address restrictions will typically prevent

creating mappings there, let's make sure uretprobe syscall checks

for that.