p2p: update documents about EXTRA_WIFI_P2P_GROUP in connection changed event

This value may be a null, receiver should check before using variable.

Bug: 137618950
Test: make docs
Change-Id: If466dac092fc345482d0456f08a915d1e7ba0010
1 file changed
tree: a3c3d3eb581f85e8db1ff85802dec46b34a9b41e
  1. framework/
  2. OsuLogin/
  3. OWNERS