src/libpcp/pdu.c: refactor for locking improvement
src/libpcp/pdu.c: refactor for locking improvement

Rework __pmRequestTimeout() to avoid previous lock nesting via the
call to __pmNotifyErr() on the error path.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp