msm: ipc: Update the check for minimum packet size

IPC Router checks for the minimum packet size of the incoming message to
be at least 32 bytes. With IPC Router version 2 header, this check is
invalid for some packets.

Update the check for the minimum incoming packet size based on the
transport on which the packet is received.

Change-Id: Iacebfe876db2e5c3513d18fcfae425ea9bd6a7cd
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>