BPF: better format for ksymaddr

The offset is now returned after a `+` symbol, instead of directly
attached to the symbol name (which made reading the output very
confusing)

Before:
    tick_do_update_jiffies64a0

After:
    tick_do_update_jiffies64+0xa0

src/python/bcc/__init__.py

@@ -732,7 +732,7 @@ def ksymaddr(addr):
  if idx == -1:
  return "[unknown]"
  offset = int(addr - ksyms[idx][1])
- return ksyms[idx][0] + hex(offset)
+ return "%s+0x%x" % (ksyms[idx][0], offset)
 
  @staticmethod
  def ksymname(name):