Changes

WIP: make 6Cxx status codes in case 2/4 ambiguous situations work

Change-Id: I968608e73057e9f57d3a89aae485d1a278e503e4

Use gsmtap_inst_fd2() to remove compiler warning

gsmtap.c: In function 'osmo_st2_gsmtap_send_apdu':
gsmtap.c:69:9: warning: 'gsmtap_inst_fd' is deprecated: Use gsmtap_inst_fd2() instead [-Wdeprecated-declarations]
   69 |         rc = write(gsmtap_inst_fd(g_gti), buf, gross_len);
      |         ^~

Change-Id: I62de38175e63cb563635a01b025b805981e4b7a9