ub: ubcore add get_mtu and other APIs that will be used by the driver.

driver inclusion
category: feature
bugzilla: NA
CVE: NA

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Ubcore add ubcore_get_mtu() support drivers to invoke to get mtu value.

Ubcore add other api definition (just def of api and data structure)
used by drivers:
- ubcore_create_vtp
- ubcore_destroy_vtp

Add definition of ubcore_tp:

Introduce to tp, tpg, ta:

TP: As defined in the UB protocol,
the transport layer is established between two UB ports
to provide reliability, congestion control, and multiplexing.

TPG: A transport group is established between two nodes and
contains several TPs. It fully utilizes the transmission capability of
all TPs in the TPG to implement multipathing.

TA: transaction layer in the UB protocol. It provides flexible
definitions for the TA model and supports weak transaction sequences.

Signed-off-by: Guoxin Qian <qianguoxin@huawei.com>
Signed-off-by: Yizhen Fan <fanyizhen@huawei.com>