tipc: Lower limits for number of bearers and media types

Reduces the number of bearers a node can support to 2, which can use
identical or non-identical media. This change won't impact users,
since they are currently limited to a maximum of 2 Ethernet bearers,
and will save memory by eliminating a number of unused entries in
TIPC's media and bearer arrays.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>