[API] Expose IpSecTunnelInterface#setUnderlyingNetwork

This API is required to perform MOBIKE. This API allows an IPsec
peer to change the underlying network of its established IPsec
tunnel without re-establishing the tunnel.

Bug: 169855650
Test: atest IpSecManagerTunnelTest (new tests added)
Change-Id: Ifc8ad902cbfbe4ad07e715f2fef0faa1bf9d68f3