xutils: ifpps: Move adjust_dbm_level() to only user

The function is used only in ifpps, so move it there.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
xutils: Remove prototypes for inexistent functions from header

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
xutils: tprintf: Move get_tty_size() to only user

get_tty_size() is only used inside tprintf.c, so move it there.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
xutils: stun: Replace set_timeout() by simpler inline implementation

There's only one user for set_timeout(), so inline it there and simplify
accordingly.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>