libc: set 'errno' for invalid file descriptors

Fixes #877.
File permissions for os/run/framebuffer.run
netperf: netperf w/ static ip address on linux

The netperf test configures the target Genode system for with
10.0.2.55/24. Also, nic_drv on base-linux uses the virtual ethernet
device 'tap0', which must be configured for the test user and network
address 10.0.2.1/24 on the test host like follows.

  tunctl -t tap0 -u <user running test>
  ip address add 10.0.2.1/24 dev tap
  ip link set tap0 up
thread: convenience trace methods

Implementation of declared trace methods for (null-temrinated) C string
and character buffer with given length.
Adjust tcp_terminal quota caused by nic_bridge

Nic_bridge requires more memory.