counter ABI: Fix too large stack size warning

counter ABI: Fix too large stack size warning

Fix the following warning by splitting lttng_counter_ioctl (which has a
lot of local variables in the switch/case legs) into many sub-functions.

/home/efficios/git/lttng-modules/src/lttng-abi.c: In function ‘lttng_counter_ioctl’:
/home/efficios/git/lttng-modules/src/lttng-abi.c:1227:1: warning: the frame size of 1032 bytes is larger than 1024 bytes [-Wframe-larger-than=]
 1227 | }
      | ^

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I250c78827a743c024da2e28fe807fdd5c290e686