Changes

compile_asn1_subdir: filter compiled files by .asn suffix

When I open the .asn file in vim, pySim should not attempt to read the
vim .swp file as asn.1.

	  File "/home/moi/osmo-dev/src/pysim/pySim/esim/saip/__init__.py", line 45, in <module>
	    asn1 = compile_asn1_subdir('saip')
	[...]
	  File "<frozen codecs>", line 325, in decode
	UnicodeDecodeError: 'utf-8' codec can't decode byte 0xad in position 21: invalid start byte

Related: OS#6937
Change-Id: I37df3fc081e51e2ed2198876c63f6e68ecc8fcd8