add wubot to exchange field for inlet_test case

[jcwarner]

Please modify ROMS/External/coupling_inlet_test.in from

 Nexport(waves) = 5

  Export(waves) = Wdir  \
                  Wamp  \
                  Wlen  \
                  Wptop \
                  Wpbot

 Nimport(ocean) = 5

  Import(ocean) = Wdir  \
                  Wamp  \
                  Wlen  \
                  Wptop \
                  Wpbot

to

 Nexport(waves) = 6

  Export(waves) = Wdir  \
                  Wamp  \
                  Wlen  \
                  Wptop \
                  Wpbot \
                  Wubot

 Nimport(ocean) = 6

  Import(ocean) = Wdir  \
                  Wamp  \
                  Wlen  \
                  Wptop \
                  Wpbot \
                  Wubot

This application uses the SSW_BBL and requires the bottom orbital velocity to be sent from Waves to Ocean.