net: ipa: kill IPA_TABLE_ENTRY_SIZE

Entries in an IPA route or filter table are 64-bit little-endian
addresses, each of which refers to a routing or filtering rule.

The format of these table slots are fixed, but IPA_TABLE_ENTRY_SIZE
is used to define their size.  This symbol doesn't really add value,
and I think it unnecessarily obscures what a table entry *is*.

So get rid of IPA_TABLE_ENTRY_SIZE, and just use sizeof(__le64) in
its place throughout the code.

Update the comments in "ipa_table.c" to provide a little better
explanation of these table slots.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>