eal: fix automatic loading of drivers as shared libs

eal: fix automatic loading of drivers as shared libs

When checking the loading of EAL shared lib to see if we have a shared
DPDK build, we only want to include part of the ABI version in the check
rather than the whole thing. For example, with ABI version 21.1 for DPDK
release 21.02, the linker links the binary against librte_eal.so.21,
without the ".1".

To avoid any further brittleness in this area, we can check for multiple
versions when doing the check, since just about any version of EAL implies
a shared build. Therefore we check for presence of librte_eal.so with full
ABI_VERSION extension, and then repeatedly remove the end part of the
filename after the last dot, checking each time. For example (debug log
output for static build):

  EAL: Checking presence of .so 'librte_eal.so.21.1'
  EAL: Checking presence of .so 'librte_eal.so.21'
  EAL: Checking presence of .so 'librte_eal.so'
  EAL: Detected static linkage of DPDK

Fixes: 7781950f4d38 ("eal: fix shared lib mode detection")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Sunil Pai G <sunil.pai.g@intel.com>