rmnet_rtnl_validate() was checking for upto mux_id 254, however the
rmnet_devices devices could hold upto 32 entries only. Fix this by
increasing the size of the rmnet_devices.

Fixes: ceed73a2 ("drivers: net: ethernet: qualcomm: rmnet: Initial implementation")
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Cc: Dan Williams <dcbw@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>