Only treat an ASN1_ANY type as an integer if it has the V_ASN1_INTEGER
tag: V_ASN1_NEG_INTEGER is an internal only value which is never used
for on the wire encoding.

(Imported from upstream's d4b25980020821d4685752ecb9105c0902109ab5.)

This is redundant with our fb2c6f8c85 which I
think is a much better fix (having two notions of "type" depending on whether
we're in an ASN1_TYPE or an ASN1_STRING is fragile), so I think we should keep
our restriction too. Still, this is also worth doing.

Change-Id: I6ea54aae7b517a59c6e563d8c993d0ee22e25bee
Reviewed-on: https://boringssl-review.googlesource.com/7848
Reviewed-by: Adam Langley <agl@google.com>