package/ibrdtn: fix build with gcc 11

package/ibrdtn: fix build with gcc 11

Fix the following build failure with gcc 11:

In file included from ../../ibrdtn/data/PrimaryBlock.h:30,
                 from ../../ibrdtn/data/Serializer.h:27,
                 from ../../ibrdtn/data/Block.h:29,
                 from ../../ibrdtn/data/Bundle.h:27,
                 from ../../ibrdtn/api/Client.h:26,
                 from Client.cpp:22:
/tmp/instance-0/output-1/host/bin/../arm-buildroot-linux-gnueabihf/sysroot/usr/include/ibrcommon-1.0/ibrcommon/thread/Mutex.h:43:40: error: ISO C++17 does not allow dynamic exception specifications
   43 |                 virtual void trylock() throw (MutexException) = 0;
      |                                        ^~~~~

Fixes:
 - http://autobuild.buildroot.org/results/c2d9033c68b5c1407d2cf87b98dff61958b8e7b6

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>