do not store pointer of getenv(3)

Subsequent calls to the getenv() function can be invalid.

Reference: https://www.securecoding.cert.org/confluence/display/seccode/ENV34-C.+Do+not+store+pointers+returned+by+certain+functions
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
use ipc messages instead of signals to change state

After using f5gs it has become clear that state changes are reserved for
humans, and there does not need to be easy way of making state changes to
happen from other software.  Signals are arguably a lot easier to send
than ipc messages, but the signals are also more difficult to keep under
control.  See reference for more complete explanation why this change
makes sense.

Reference: https://www.securecoding.cert.org/confluence/display/seccode/SIG02-C.+Avoid+using+signals+to+implement+normal+functionality
Signed-off-by: Sami Kerola <kerolasa@iki.fi>