lwip: add checksum options to 'lwipopts.h'

This patch adds some of lwip's checksum calculation options to the
Genode-specific 'lwiptops.h' configuration file. The checksum calculations
are enabled by default.

Fixes #868.
nic_bridge: cache card's MAC address (Fixes #869)
Increase default NIC session's queue size (fix #870)
core: explicitly throw Out_of_metadata

In case there is not enough quota left to create the trace buffer
or trace policy dataspace throw Out_of_metadata explicitly instead
of rethrowing the Ram_session::Quota_exceeded exception. Now one
can catch Trace::Out_of_metadata exception in a client application.

In addition fix Allocator_guard::withdraw() checks because this
method does not throw any exceptions and a failed withdrawal goes
unoticed.

Fixes #871.
CPU affinity configuration fixes

- if no affinity was set for a new thread before calling
  Cpu_session::start(), the CPU session's affinity gets set for this
  thread
- documentation fix: <affinity_space> -> <affinity-space>

Fixes #873.
lwip: fix thread reset value in 'sys_arch_unprotect()'

Fixes #866.
usb_drv: initialize '_tx_alloc' variable

Fixes #867.