msm: ipa: fix HW path IPv6 RNDIS DL transfer failure

Headers in the IPA HW table must be word-aligned. Commit
a439c510 broke the logic
that ensures this. This caused malformed RNDIS packets to
be received (and discarded) at host. This commit fixes that
bug.

Change-Id: I9ecd1e5b3b272b1c625be3aab9a5eb5b614e2e7b
Signed-off-by: Ravi Gummadidala <rgummadi@codeaurora.org>