Fix potential OOB write in btm_read_remote_ext_features_complete

Add event length check to avoid hci event sent from controller not
correct.
Add page number check to avoid page number is bigger than
HCI_EXT_FEATURES_PAGE_MAX.

Bug: 141552859
Bug: 144205318
Test: inject function
Merged-In: Iaca4db4ee9bf27362f62aba0da088727e98955d1
Change-Id: Iaca4db4ee9bf27362f62aba0da088727e98955d1